Copyright: Copyright Digital Equipment Corporation 1992, 1993


Help Index
RAID Evaluator Help Index	1 of 2

Commands

File Menu

Workload Menu

Windows Menu

Parameters Menu

Help Menu

Glossary

Disk Array-Related Terms

Concepts and Procedures

RAID Evaluator Application Windows

Creating a new Workload

Editing an Existing Workload

Computing a C-A-P Analysis

Working with Bar Graph Windows

Working with Request/Response Curves

Comparing C-A-P Analyses

Working with Workload Files

Modifying Controller and Disk Parameters

Quitting

Available From Your Application

Context Sensitive Topics


RAID Evaluator Help  Index	2 of 2

Sample Fonts

Windows system fonts

Sample Graphics

Bitmaps by reference

Visually placed bitmap

Keyboard Topics

Windows Keys

Design Ideas

Computer Based Training

Simulation

Having Fun

Children's Game


The Index contains a list of all Help topics available for the RAID Evaluator program. For information on how to use Help, press the F1 key or choose Using Help from the Help menu.


File Menu

The File menu contains the commands that enable you to manipulate entire Workload files and Result Text files, In addition, it contains the Exit command by which you exit from the RAID Evaluator program.

For more information on an individual File menu command, select the command of interest by name.Temporary Workload File Causes a temporary Workload file to be created.

Open Workload File... Causes an existing permanent Workload file to be opened.

Close Workload File Causes the currently active Workload file to be deactivated.

Save Workload File Causes the Workloads in memory to be saved in a permanent Workload file.

Save Workload File As... Causes the Workload in memory to be saved in a new Workload file. If you supply this command with the name of an existingWorkload file, the Workload file is overwritten.

Delete Workload File Permanently deletes the active Workload file from disk and memory. Use this command with caution, since it completely eliminates all Workload data stored in the file.

Open Result Text File Activates a Result Text file. Enables Write buttons on any C-A-P Analysis window  and the writing of C-A-P Analysis results to the active Result Text file.

Close Result Text File Deactivates the active Result Text file. Disables the writing of C-A-P Analysis results in text form for later editing.

Exit Exits from the RAID Evaluator program. Deactivates the active Result Text file (if there is one) and closes the active Workload file (if there is one).Workload Menu

The Workload menu contains the commands that enable you to work with individual Workloads  stored in your personal computer's main memory. Commands on the Workload menu do not affectWorkloads stored in files on disk.

For more information on an individual Workload menu command, select the command of interest by name.

New Workload Creates a new Workload  in memory and displays its parameters in the Input panel .

Using this command is identical to clicking the New Workload button in the Input panel.

Select Workload... Enables you to select one of theWorkloads stored in memory for display in the Input panel.

Using this command is identical to pulling down the Workload Name list box in the Input panel and selecting a Workload name from it.

Set Default Workload Values Sets the default Workload parameters to those currently displayed in the Input panel. Default Workload parameters are those initially supplied when you create a new Workload in memory.

Delete Single Workload from Memory Enables you to delete one Workload from memory.

This command has no effect on the contents of Workloads stored in files on disk.

Delete All Workloads from Memory Deletes all Workloads currently stored in memory. A message box requests that you verify the deletion. If you respond affirmatively, Workload memory is cleared; If you respond negatively, the operation is cancelled, and your Workloads remain intact.

When you delete all Workloads from memory, the Input panel automatically displays a new Workload with the name Workload No. 1 and with the current default parameters.

This command has no effect on the contents of Workloads stored in files on disk.


Windows Menu

The Windows menu contains commands that enable you to manipulate groups of output windows within the RAID Evaluator main window.

For more information on an individual Windows menu command, select the command of interest by name.

Cascade Output Windows Causes multiple C-A-P Analysis windows  to be cascaded, or arranged in a diagonally overlapping row with their titles visible.

Close Output Windows Closes all open C-A-P Analysis windows  and any child Bar Graph or Request/Response Curve windows they may have.

Cascade Bar Graph Windows  Causes multiple Bar Graph windows to be cascaded, or arranged in a diagonally overlapping row with their titles visible.

Close Bar Graph Windows Closes all open Bar Graph windows. Does not affect parent C-A-P Analysis windows.

Plot Bandwidths Causes bar graphs of Bandwidth to be plotted in all existing Bar Graph Windows. Does not cause new Bar Graph windows to be created.

Plot Request Rates Causes bar graphs of Request Rate (Thruput) to be plotted in all existing Bar Graph Windows. Does not cause new Bar Graph windows to be created.

Plot Relative Data Reliabilities Causes bar graphs of Relative Data Reliability (where the reliability of a single disk is taken to be 1.0) to be plotted in all existing Bar Graph Windows. Does not cause new Bar Graph windows to be created.

Cascade Curves Windows Causes multiple Request/Response Curve windows to be cascaded, or arranged in a diagonally overlapping row with their titles visible.

Close Curves Windows Closes all open Request/Response Curve windows. Does not affect parent C-A-P Analysis windows.

Compare Displayed Curves Causes a Comparison window containing the request/response curves for a single RAID Level from all existing Request/Response Curve windows to be displayed.


Parameters Menu

The Parameters menu contains commands that enable you to modify the performance characteristics of User-Defined Disks and Controllers for use in the RAID Evaluator model.

For more information on an individual Parameters menu command, select the command of interest by name.

Controllers... Causes a Controller Definition dialog box to be displayed, and allows entry of new User-Defined Controller parameters or modification of existing User-Defined Controller parameters.

Disks... Causes a Disk Definition dialog box to be displayed, and allows entry of new User-Defined Disk parameters or modification of existing User-Defined Disk parameters.

Note: Parameter values for some Digital-supplied disk and controller models are built into the RAID Evaluator program. These parameter values have been obtained based on Digital's actual experience with the devices in question, and cannot be modified.


Help Menu

The Help menu invokes the Microsoft Windows Help facility using this help file.

For more information on an individual Help menu command, select the command of interest by name.

About 	Causes a modal dialog box containing the version of the RAID Evaluator program that is running and some descriptive information about the program to be displayed. Click the OK button in this dialog box to dismiss it and return to the RAID Evaluator session.

Index 	Invokes this Help facility. If the Help facility is already running, it becomes the active task, and the root index is displayed. Click any of the index entries on which the cursor turns into a hand with an extended index finger to display information about that topic.


Glossary

Non-highlighted terms in this glossary are to be defined in a future version of RAID Evaluator Help.

RAID Evaluator Files

Workload file

Result Text file

RAID Evaluator Windows

Bar Graph window

C-A-P Analysis window

Input panel

Configuration Comparison window

Request/Response curve window

RAID Evaluator Concepts

C-A-P Analysis

I/O Profile

Load Balance

Locality of Reference

Read/Write Balance

Workload

Workload name

Storage and RAID Concepts

Adapter

Array

Controller

Disk

Disk Drive

Independent Disks

RAID	RAID Level

RAID 0	RAID 1	RAID 3 	RAID 5 	RAID 0+1

Reconstruction

Regeneration

Storage Element

Subsystem

Virtual Disk


Copying Text
RAID Evaluator Windows

The RAID Evaluator program operates by accepting input data or displaying results in any of several windows.

The RAID Evaluator main window encloses the entire program session. It is a typical Microsoft Windows top-level application window which you can maximize (enlarge to fill your entire screen) or minimize (shrink to an icon on your windows desktop), and from which you can access windows system functions via a system menu in the upper left-hand corner. All other RAID Evaluator windows are child windows of the main window. Their contents never extend outside the boundaries of the main window. When you shrink the RAID Evaluator main window to an icon, all of its contents are shrunk with it.

The RAID Evaluator Input panel is a Microsoft windows dialog box. You supply all new input data to the RAID Evaluator program through this window. The Input panel appears in the upper left-hand corner of the RAID Evaluator main window. It cannot be moved within the main window, nor may you change its size or minimize it.

The C-A-P Analysis window is the RAID Evaluator program's primary output. When you click the Compute C-A-P button in the Input panel, a C-A-P Analysis window appears displaying a comparison of the relative cost, availability, and performance of the active Workload when implemented with each of the six RAID Levels supported by the RAID Evaluator program. Up to four C-A-P Analysis windows may be displayed at any instant. If you attempt to display a fifth, a message box suggests that you close an existing C-A-P Analysis window to make room for the new one.

C-A-P Analysis windows may be minimized and rezised in both the horizontal and vertical directions. The RAID Evaluator program chooses an initial size for new C-A-P Analysis windows based on the resolution of your monitor. Each C-A-P Analysis window contains the name of the Workload (taken from the Workload Name field in the Input panel) in its title bar or icon.

The Bar Graph window is an optional child window of the C-A-P Analysis window. It displays performance (bandwidth or request rate) or relative data reliability data from the C-A-P Analysis window in graphical form. You create a Bar Graph window by clicking the Graph button in a C-A-P Analysis window. Buttons in the Bar Graph window control which datum is displayed. Bar Graph windows may be resized, minimized or closed. When you close a C-A-P Analysis window, its Bar Graph window, if any, is automatically closed as well.

The Request/Response Curve window displays the Response times of the six supported RAID Levels as a function of the arrival rate of I/O requests. These curves can give you a feeling for how rapidly responsiveness will degrade as a configuration approaches saturation. By clicking check boxes in the Request/Response window, you can cause display of the curves for individual RAID Levels to be suppressed. This can be useful if you wish to see greater detail for the lower-performance models, since each time you change the display, the scale is recomputed and the graphs are redrawn.


Copying Text
Creating a New Workload

You create a new Workload by clicking the New Workload button in the Input panel  or by selecting the New Workload option in the Workload menu. A new Workload with parameters equal to the current defaults replaces whichever Workload had been displayed in the Input panel.

The name of the new Workload is Workload No. n, where n is the smallest positive integer not already in use in a Workload name of this form. You may change the new  Workload name to any unique character string of up to 48 characters by using the mouse or the tab key to set the input focus in the Workload name box and editing the text in the box.

If you have activated a temporary Workload file (by clicking Temporary Workload File on the File menu), each Workload is saved on disk when you create it and every time you modify it. If, however, you are using a permanent Workload file, new Workloads are not saved on disk until you explicitly save them using the Save Workload File or Save Workload File As... commands.

If you intend to create several Workloads with similar parameters, you should create one with the most common parameter values, and then use the Set Default Workload Values option in the  Workload menu. When you create each new Workload, it initially has the common default values.


Deleting Text
Editing an Existing Workload

You can edit any Workload in memory by making it the current Workload. You make a Workload the current one by pulling down the Name list box in the Input panel and double-clicking its name. This causes its parameters to be displayed in the Input panel.

You can move from field to field in the current Workload either by moving the mouse to the field you want to edit and clicking, or by using the TAB key to advance sequentially through the fields.

Note: you must use the mouse to edit the Single Disk MTTR (hr) field; the tab key will not cause this field to be selected.

Once the focus is in the field you wish to edit, you use the standard Microsoft Windows editing keys and mouse actions to change the field's contents. Changes you make to a field do not take effect until you move the input focus elsewhere on the desktop. When you move the input focus (e.g., by using the TAB key or by clicking another field), the change becomes part of the Workload's memory image. Unless there is a temporary Workload file active, however, the change does not become part of the Workload's permanent disk image until you use the Save Workload File (As...) option on the File menu.

Editing a Workload does not immediately cause its C-A-P Analysis to be recomputed. To recompute a Workload's C-A-P Analysis after you change a parameter, click the Compute C-A-P button in the Input panel. This causes recomputation of the C-A-P Analysis for the current Workload, and updating of any associated output windows (C-A-P Analysis, Bar Graph, and Request/Response Curve, if the latter two exist).


Exiting
Exiting (Quitting)

You can exit from the RAID Evaluator application in any of 4 ways:

By hitting the ESC key when any field in the Input panel  has the focus.

By clicking the Quit Execution button in the Input panel.

By selecting Exit from the File menu.

By selecting Close from the RAID Evaluator main window's System Menu.

Whichever method you use, if there is an active Workload file, a message box appears offering you the chance to continue execution instead of quitting. If you elect to continue quitting, and the active Workload file has unsaved changes, another message box appears requiring you to choose between saving the changes and not saving them.


Edit Clear Command
Computing a C-A-P Analysis

You compute a C-A-P Analysis by clicking the Compute C-A-P button on the Input panel . When you click this button, and a C-A-P Analysis window  already exists for the current  Workload, the data in it are updated to reflect any changes you have made to data in the Input panel. If a child Bar Graph or Reequest/Response Curve exists for the C-A-P Analysis window, these are updated also.

If no C-A-P Analysis window exists for the current Workload, a new one is created. You may display up to four C-A-P Analysis windows in the main window at any one time. To make room for a new C-A-P Analysis window when the maximum of four are already displayed, you must close one of the existing ones by clicking its Close button.


Edit Copy Command
Working with Bar Graphs

Each C-A-P Analysis window  contains a Graph button which can be used to display the either Thruput (request rate at the specified required response time), Bandwidth, or Relative Cost values for each of the RAID Levels in the C-A-P Analysis in bar graph form. The bar graph conveys no information beyond what is displayed in the C-A-P Analysis window, but can give a more vivid interpretation of the differences between different RAID Levels because it is graphical.

Each Bar Graph window is a child of a C-A-P Analysis window. If you close a C-A-P Analysis window with an associated Bar Graph window, the Bar Graph window closes as well. A Bar Graph window can be shrunk to an icon independently of its parent C-A-P Analysis window.

The Bar Graph window has four buttons of its own:

The Close button closes the Bar Graph window. It has no effect on the Bar Graph window's parent C-A-P Analysis window.

The Rqst. Rate button causes the Workload's request rates under the various RAID Levels to be displayed in the bar graph window.

The Bandwidth button causes the Workload's bandwidths under the various RAID Levels to be displayed in the Bar Graph window.

The Data Rel. button causes a Workload's relative data reliability under the various RAID Levels to be displayed. Data reliability is always shown normalized. For Thruput-intensive Workloads, this means that the Independent Disk and RAID 0 data reliabilities always have the value 1.  (RAID Evaluator Data Reliability computations assume that the loss of any single disk in the Workload's configuration is tantamount to the loss of all disks.)

Other data reliabilities are computed and displayed in terms of the Independent Disk data reliability. For example, a value of 3,000 for RAID 1 data reliability means that if the Workload's storage capacity is provided in the form of RAID 1 arrays (shadow sets), the data reliability will be 3,000 times as great as that of an equivalent amount of user-accessible storage provided on independent disks.


Edit Copy Command
Working with Request/Response Curves

Each C-A-P Analysis window  contains a Curve button which can be used to display Response Time plotted as a function of Request Rate for each of the RAID Levels in the C-A-P Analysis.

Each Request/Response curve window is a child of the C-A-P Analysis window from which it is spawned. If you close a C-A-P Analysis window, the corresponding Request/Response curve window closes as well. A Request/Response curve window can be shrunk to an icon independently of its parent C-A-P Analysis window.

Unlike the Bar Graph window , the Request/Response curve window conveys more information than is found in the C-A-P Analysis. As the load presented to a complex I/O subsystem (expressed in number of requests per second) increases, queues begin to build up at various points in the subsystem (the bottlenecks), and the elapsed time required to completely process a given request (the response time) increases, although the actual processing time not. The variation of response time as a function of average request rate is plotted in the Request/Response curve window.

Request/response curves can be useful in giving you a feeling for how subsystem responsiveness degrades as the subsystem request load presented to the subsystem approaches its saturation point. Especially interesting is the knee of the curve; the region in which it changes from being predominantly horizontal to predominantly vertical. In this region, minor increases in request load can result in major changes in responsiveness. If you are designing an I/O subsystem, you want to approach the knee (by manipulating the configuration to minimize cost), but stay to the left of it (or else response time becomes very susceptible to momentary peaks in request load).

You can use the Configuration Comparison window to compare the effect of changes in configuration or I/O profile on a single RAID Level.


Comparing Curves
Comparing the Request/Response Curves of Two or More C-A-P Analyses

Once you have created two or more Workloads in memory computed C-A-P Analyses, and displayed request/response curves for them, you can compare the Workloads' request/response curves with each other by clicking the Comparison button on the Input panel . or the Compare Displayed Curves command on the Windows menu.

When you click the Comparison button, a Configuration Comparison window  appears displaying the Independent Disk request/response curves for all existing request/response curve windows.

You may change the curves displayed in the Configuration Comparison window to compare the Workloads for any other single RAID Level by clicking the corresponding radio button. Only one RAID Level at a time can be displayed in the Configuration Comparison window.


Edit Paste Command
Working with Workload Files

The RAID Evaluator program can store groups of Workloads permanently in files. This means that you can save your work from a RAID Evaluator session and recall it in a later session rather than recreating it.

Some Workload file containing typical Workloads are included with the RAID Evaluator program. To access these, use the Open Workload file... command on the File menu. This creates a dialog box listing the names of the files supplied with the RAID Evaluator program.

When you open, or activate, a RAID Evaluator Workload file, the Workloads in it are read into memory, replacing any Workloads that had been previously stored. One of these Workloads to be the active Workload at any instant, but all are accessible, so you can quickly switch from one to another.

You can compute C-A-P analysis of the active Workload, producing a C-A-P Analysis window. The C-A-P Analysis window continues to exist if you make another Workload the active one. You can have up to four C-A-P Analysis windows displayed (or minimized) at any instant, so you can easily compare the results of two scenarios.

You can also create your own Workload files. Create a set of Workloads using the New Workload button on the Input panel and modifying each new Workload to reflect the parameters you desire. When you are satisfied with the set of Workloads in memory, use the Save Workload File As... command from the File menu to save your work permanently in a file.

Refer to the File menu overview and individual command descriptions for detailed information on manipulating Workload files.


Modifying Parameter Values
Changing Disk and Controller Parameters

The RAID Evaluator program supports both Built-in Disks and Controllers, whose performance parameter values are coded into the program and cannot be changed by the user, and User-Defined Disks and Controllers, whose parameter values may be supplied and modified by the user.

The Parameter Menu is used to manipulate User-Defined Disk and Controller parameter values.

The Parameter Menu contains two commands, Controller..., and Disk..., which are used to modify the User-Defined Controller and Disk databases respectively. Selecting these commands causes the Controller Definition and Disk Definition dialog boxes respectively to pop up. These dialogs can be used either to supply new parameter values for existing User-Defined Controllers and Disks, or to define new User-Defined Controllers and Disks. In either case, modifications to the RAID Evaluator parameter database do not take effect until the program has been stopped and restarted.


File New Command
File Menu: Temporary Workload File Command

This command allows you to create a temporary Workload file.

When a temporary Workload file is active, every Workload you create in memory is automatically written to it after every modification. While this causes higher execution overhead, your Workloads are saved on your hard disk with no effort on your part.

You can make a temporary Workload file permanent by using the Save Workload File As...  command on the File menu. Once you make a temporary Workload file permanent by giving it a name, it is subject to the normal rules for Workload files. In particular, no changes to the Workloads in the file are permanent (i.e., saved on disk so that they persist across sessions) until you explicitly save the file on disk using the Save command on the File menu.

Once a Workload file has been saved, the RAID Evaluator program no longer uses a temporary Workload file (until you use the New Workload File... command to create another temporary Workload file). It does not, however, delete temporary Workload files from the hard disk. You may wish to delete temporary Workload files periodically.

The RAID Evaluator program stores temporary Workload files in your Windows default directory. They have names in the form: ~REV***.WLD, where *** is a 3-character string chosen by Microsoft Windows to guarantee uniqueness. Once you have saved a Workload file under a permanent name, you may delete the corresponding ~REV***.WLD file from your Windows default directory.


File Menu Open Command
File Menu: Open Workload File... Command

Use this command to open an existing permanent Workload file or to create a new one.

This command causes a Select File dialog box to appear. The Select File dialog allows you to select a directory and specify which file in that directory to open.

The default MS-DOS file type for Workload files is .WLD, although you may use any valid MS-DOS file type.

Files in the current directory with the file type .WLD are displayed when the Select File dialog box is initially opened. A Directories list box is provided to allow you to navigate among multiple storage facilities. You may also type the name of a file in the Select File dialog box's Current File edit box.

When it opens an existing Workload file, the RAID Evaluator program checks the file's format to ascertain that it actually contains Workload descriptions. The program will not open a file that does not contain valid Workload descriptions.


File Menu Open Command
File Menu: Close Workload File Command

Use this command to close an existing temporary or permanent active Workload file. If the active Workload file is permanent and changes have been made to Workloads in memory since it was last saved, a message box requests that you explicitly decide to save the current Workload memory images as the Workload file or discard them. If you elect to save the current memory images, they overwrite the previous contents of the Workload file on disk. If you elect not to save, the contents of the Workload file remain as they were, and the Workloads currently in memory are discarded.

In either case, a second message box informs you when the Workload file has been closed.

After you use this command, there is no active Workload file. This fact is recorded in the title bar of the Input panel .


File Save Command
File Menu: Save Workload File Command

Use this command to save changes to made to Workloads in memory in an existing active file on your hard disk. This command may only be used when there is an active Workload file.

If you wish to save the Workloads currently in memory (whether or not you have created a temporary file) in a new permanent Workload file, use the Save Workload File As... command, and supply the name of the file to be created.


File Save As Command
File Menu: Save Workload File As... Command

Use this command to create a new Workload file on a disk and save the Workloads in memory in it. This command may only be used when there is an active Workload file.

This command causes a Select File dialog box to appear. The Select File dialog allows you to select a directory and specify which file in that directory to open.

The default MS-DOS file type for Workload file  is .WLD, although you may use any valid MS-DOS file extension.

Files in the current directory with the file type .WLD are displayed when the Select File dialog box is initially opened. A Directories list box is provided to allow you to navigate among multiple storage facilities. You may also type the name of a file in the Select File dialog box's Current File edit box.

If you type the name of an existing file, a dialog asks you to verify that the existing file should be overwritten. If you answer yes, the file's previous contents are destroyed. If you answer no, the save operation is abandoned.


File Save As Command
File Menu: Delete Workload File Command

Use this command to delete the active Workload file from the disk. This command may only be used when there is an active Workload file.

Use this command with caution, since it permenently erases all of the Workload data stored in the active Workload file from both memory and disk.


File Save As Command
File Menu: Open Result Text File Command

Use this command to activate an existing Result Text file or to create a new one on a disk. When you open an existing Result Text file, the RAID Evaluator program checks for a recognizable signature to minimize the probability of writing over another application's file. The program will not open an existing Result Text file that does not have a valid signature.

When you activate either a new or existing Result Text file, the Write buttons of any C-A-P Analysis windows are enabled, and you can write the contents of a C-A-P Analysis window to the active Result Text file by clicking the button.

The program always appends new data to the end of the active Result Text file, so you do not lose results from previous sessions when you activate an existing Result Text file.


File Save As Command
File Menu: Close Result Text File Command

Use this command to deactivate the active Result Text file. When no Result Text file is active, the Write buttons of any C-A-P Analysis windows  are disabled, and you cannot write C-A-P Analysis results to a text file.


File Menu Quit Command
File Menu: Quit Command

Use this command to exit from the RAID Evaluator program.

If there is an active Workload file, a message box gives you the option of either continuing execution or completing the quit operation.

If you elect to continue quitting, and there are unsaved changes to the active Workload file, a second message box requests that you either save the changes or acknowledge that you do not wish to save them.

Your active Result Text file, if there is one, is always closed automatically. In fact, since the program opens the active Result Text file only when you write to it, and closes it immediately thereafter, you can open the active Result Text file in Notepad or another editor at any time except when you are actually writing to it from a C-A-P Analysis window .

Using this command is identical to clicking the Quit Execution button in the Input Panel.


Workload Menu New Workload Command
Workload Menu: New Workload Command

New Workload Button on Input Panel

Use this command to create a new Workload  in memory and display its parameters in the Input panel . The new Workload becomes the active one. Creating a new Workload does not affect the Workload which was previously displayed in the Input panel; its image remains in memory available for subsequent recall.

Using this command is identical to clicking the New Workload button in the Input panel.


File Menu Quit Command
Workload Menu: Select Workload... Command

Use this command to select one of the Workloads in memory to become the active Workload. When you click this command, the program displays a Choose Workload dialog to enable you to select one of the Workloads in memory for display in the Input panel .

The names of all Workloads in memory are displayed in a list box in the Choose Workload dialog. Click one of the names and then click the OK button to select a Workload for display in the Input panel. Alternatively, double-click the Workload name. In either case, the Input panel immediately displays the parameters of the selected Workload.

Using this command is identical to pulling down the Name list box in the Input panel and selecting a Workload name from it by double-clicking.

If the C-A-P Analysis for a Workload is currently displayed in a C-A-P Analysis window, the text "-- Displayed" appears beside its name whenever it appears in either of these list boxes.


File Menu Quit Command
Workload Menu: Set Default Workload Values Command

Sets the default Workload  parameters to those currently displayed in the Input panel . Default Workload parameters are those initially supplied when you create a new Workload in memory.

Hint: If you need to create several Workloads that differ from each other in only one or two parameters, set the Input panel  contents to represent one of them and then use this command. When you create subsequent Workloads (using the New Workload command on the Workload menu or the New Workload button in the Input panel), the new Workload will have nearly all of the required parameter values.


File Menu Quit Command
Workload Menu: Delete Single Workload from Memory Command

Use this command to delete one Workload  from memory. Clicking this command causes a Choose Workload dialog to be displayed. Click one of the Workload names in the dialog to select it for deletion, and then click OK, or just double-click the name. A message box asks you to verify that you really want to delete the selected Workload from memory. If you respond affirmatively, the Workload is deleted from memory; If you respond negatively, the operation is cancelled.

This command has no effect on Workloads stored in files on disk. If you use this command to delete the memory image of a Workload stored in a permanent Workload file, you can still retrieve the Workload by activating the Workload file that contains it.


File Menu Quit Command
Workload Menu: Delete All Workloads from Memory Command

Use this command to delete all Workloads  currently stored in memory. A message box requests that you verify the deletion. If you respond affirmatively, Workload memory is cleared; If you respond negatively, the operation is cancelled, and your Workloads remain intact.

When you delete all Workloads from memory, the Input panel  displays a new Workload with the name Workload No. 1 and with the current default parameters.

This command has no effect on the contents of Workloads stored in files on disk. If you use this command to delete the memory image of the Workloads stored in a permanent Workload file, you can still retrieve the Workloads by activating the Workload file that contains them.


File Menu Quit Command
Windows Menu: Cascade Output Windows Command

Use this command to arrange C-A-P Analysis windows diagonally overlapping each other in the lower left-hand area of the main window.

This command is useful when you have several C-A-P Analysis windows displayed and some of them are occluded by others, blocking your view of them. The command arranges all existing C-A-P Analysis windows so that you can see their titles. You can then bring the one you would like to study to the front by clicking its title bar.

If you have minimized or resized any C-A-P Analysis windows, this command also restores them to the default size for your monitor's resolution.

This command does not affect other output windows displayed in the main window, except that it may cause C-A-P Analysis windows to occlude them.


File Menu Quit Command
Windows Menu: Close Output Windows Command

Use this command to close all existing C-A-P Analysis windows and their child Bar Graph windows and Request/Response Curve windows, if any exist.


File Menu Quit Command
Windows Menu: Cascade Bar Graph Windows Command

Use this command to arrange Bar Graph windows diagonally overlapping each other in the lower right-hand area of the main window.

This command is useful when you have several output windows displayed and some of them are occluded by others, blocking your view of them. The command quickly arranges all existing Bar Graph windows so that you can see their titles. You can then bring the one you would like to study to the front by clicking its title bar.

If you have minimized or resized any Bar Graph windows, this command also restores them to the default size for your monitor's resolution.

This command does not affect other output windows displayed in the main window, except that it may cause Bar Graph windows to occlude them.

Bar Graph windows and C-A-P Analysis windows are cascaded in such a way that their titles do not completely occlude each other when this command and the Cascade Output Windows command are used in succession.


File Menu Quit Command
Windows Menu: Close Bar Graph Windows Command

Use this command to close all Bar Graph windows without affecting other output windows that may be displayed in the main window. This command causes Bar Graph windows to close whether they are displayed or minimized.

You can re-open a closed Bar Graph window as long as its parent C-A-P Analysis windows is displayed by clicking the Graph button in the C-A-P Analysis window.


File Menu Quit Command
Windows Menu: Plot Bandwidths Command

Use this command to plot bar graphs representing bandwidth for all RAID levels supported by the RAID Evaluator program in all existing Bar Graph windows.


File Menu Quit Command
Windows Menu: Plot Request Rates Command

Use this command to plot bar graphs representing thruput (request rate at the response time specified in the Input panel) for all RAID levels supported by the RAID Evaluator in all existing Bar Graph windows.


File Menu Quit Command
Windows Menu: Plot Relative Data Reliabilities Command

Use this command to plot bar graphs representing relative data reliability for all RAID levels modeled by the RAID Evaluator in all existing Bar Graph windows.

Relative Data Reliability is expressed relative to the reliability of a single disk. In both the C-A-P Analysis window and the Bar Graph window, the reliability of a single disk is shown as 1. The data reliability of other RAID Levels is shown as a multiple of single disk reliability. Thus, if a certain type of disk is known to have a Mean Time Between Failures of 100,000 hours, and the RAID Evaluator program shows that the relative data reliability for an array of these disks is 1,000, the Mean Time Between Data Loss (MTBDL) of the array is 100,000,000 hours.

Note two things about the RAID Evaluator program's calculation of MTBDL:

1.	MTBDL calculated by the RAID Evaluator program is the mean time between data loss due to disk failure only. Other factors not modeled, such as subsystems, buses, environment, applications, etc., can affect actual MTBDL.

2.	Loss (destruction) of data is different from loss of availability of data to applications. RAID 1, 3, and RAID 5 by themselves will protect against permanent loss of data to a very high degree. To provide continuous application access to data in the face of component failures requires that RAID arrays be augmented with other high-availability techniques, such as redundant controllers, host adapters, and data paths, and supporting software to provide automatic switchover to alternate components in the event of a failure.


File Menu Quit Command
Windows Menu: Cascade Curves Windows Command

Use this command to arrange C-A-P Analysis windows diagonally overlapping each other in the lower left-hand area of the main window.

This command is useful when you have several C-A-P Analysis windows displayed and some of them are occluded by others, blocking your view of them. The command quickly arranges all existing C-A-P Analysis windows so that you can see their titles. You can then bring the one you would like to study to the front by clicking its title bar.

If you have minimized or resized any C-A-P Analysis windows, this command also restores them to the default size for your monitor's resolution.

This command does not affect other output windows displayed in the main window, except that it may cause C-A-P Analysis windows to occlude them.


File Menu Quit Command
Windows Menu: Close Curves Windows Command

Use this command to close all Request/Response Curve windows without affecting other output windows that may be displayed in the main window. This command causes Request/Response Curve windows to close whether they are displayed or minimized.

You can re-open a closed Request/Response Curve window as long as its parent C-A-P Analysis windows is displayed by clicking the Curve button in the C-A-P Analysis window.


Parameters Menu Controller Command
Parameters Menu: Drive... Command

Use this command to add new User-Defined Disks to the RAID Evaluator hardware parameter database. This command causes a Disk Definition dialog box to appear, and allows either input of new disk types or modification of the parameters of existing types.

When User-Defined Disk parameters are modified, or when new User-Defined disk types are defined, The RAID Evaluator program must be stopped and restarted in order for the new data to be used in calculations.


Parameters Menu Drive Command
Parameters Menu: Drive... Command

Use this command to add new User-Defined Disks to the RAID Evaluator hardware parameter database. This command causes a Disk Definition dialog box to appear, and allows either input of new disk types or modification of the parameters of existing types.

When User-Defined Disk parameters are modified, or when new User-Defined disk types are defined, the program must be stopped and restarted in order for the new data to be used in calculations.


File Menu Quit Command
Help Menu: About Command

Use this command to ascertain which version of the RAID Evaluator program you are executing. It displays an application modal dialog box containing the program name and version number (both of which may change from version to version).of the currently executing image, and some information about authorship.

Since this dialog is application modal, you cannot perform any other actions in your RAID Evaluator session until you dismiss it by clicking the OK button. You can, however, move the input focus to other applications' windows and execute them while the About dialog is present.


File Menu Quit Command
Help Menu: Index Command

Use this command to invoke this Help facility, or, if this Help facility is already executing, to display the top-level index of RAID Evaluator help topics.


Context Sensitive Topics

This Help system includes topics that you can call directly from the Helpex sample application. To get context-sensitive help from Helpex, press Shift+F1 and click on any element of the Helpex application window. You can also highlight any Helpex menu command using the keyboard and press F1 to get help on the command. Each topic has a unique context identifier, listed in the [MAP] section of the Help project file:

[MAP]

#define HELPID_EDIT_CLEAR     100

#define HELPID_EDIT_COPY      101

#define HELPID_EDIT_CUT       102

#define HELPID_EDIT_PASTE     103

#define HELPID_EDIT_UNDO      104

#define HELPID_FILE_EXIT      200

#define IDM_F_NEW       201

#define HELPID_FILE_OPEN      202

#define HELPID_FILE_PRINT     203

#define HELPID_FILE_SAVE      204

#define HELPID_FILE_SAVE_AS   205

#define HELPID_EDIT_WINDOW    300

#define HELPID_MAXIMIZE_ICON  301

#define HELPID_MINIMIZE_ICON  302

#define HELPID_SYSTEM_MENU    305

#define HELPID_SIZING_BORDER  307


Edit Window

The edit window in the sample application really doesn't let you edit anything.


Maximize Icon

Use the maximize icon (the upward pointing arrow at the right-hand end of the main window title bar) to expand the RAID Evaluator main window to fill your entire screen. This may be useful if you are comparing multiple Workloads to each other.


Minimize Icon

Click the minimize box to shrink the main window to an icon. This may be useful if you wish to do something else momentarily, but you expect to use the RAID Evaluator program again soon,and you don't want to lose your context of Workloads.

All of the sub-windows that appear within the main window except the Input panel  may be shrunk to icons. Each type of window (C-A-P Analysis, Bar Graph, Request/Response, and Comparison) has its own icon design to enable you to distinguish easily among them.

When you choose one of the Cascade commands from the Windows menu, all of the windows to be cascaded are restored to a normalized size.


Sizing Border

The RAID Evaluator main window is resizable. This means that you can move the mouse cursor (the upward right pointing arrow) to the window's border where it will turn into a double-headed arrow. While the mouse cursor is a double-headed arrow, you can click-hold with MB1, and the  main window will resize as you move the mouse.

All of the sub-windows that appear within the RAID Evaluator main window except the Input panel  are also resizable.


System Menu

This topic describes the system menu.


Required User Capacity
Req'd User Capacity (GBytes)

Use this field to specify the user-accessible storage capacity required for this Workload .

The RAID Evaluator program uses the value you supply in this field along with the Disk Type and Disk Utilization (%) values to compute the number of disks required, according to the following formula:

Disks Required = Req'd User Capacity / (Disk Utilization * 100) / Single-Disk Capacity

Allowable values for this field are between 0.1 GBytes (i.e., 100 MBytes) and 1,000 GBytes (i.e., 1 TByte). If you enter too small or too large a value in this field, a Message Box informs you of the allowable limits, and the Compute C-A-P button is greyed until you correct the invalid value.


WorkloadName
(Workload) Name

Use this field to select a Workload  to become the active one or to give the active Workload a descriptive name of up to 48 bytes in length. The name may be any character string you choose.

If you pull down the list of Workloads in memory (by clicking the downward-pointing arrow to the right of the edit box) the name of the active Workload is highlighted. You select another Workload for activation by clicking its name.

When you create a new Workload, the RAID Evaluator program automatically assigns it a name of the form Workload No. X, where X is the smallest integer that will result in a unique Workload name.

You may give a Workload a more descriptive name by:

1.	making it the active one.

2.	clicking the Name edit box (this highlights the current Workload name).

3.	typing the new name.

Note: 	If you type the name of an existing Workload, the program makes that Workload the active one. Duplicate Workload names are not possible.


Disk Type

Use this field to specify the disk type for the active Workload. The current version of the RAID Evaluator program only models homogeneous configurations, i.e., configurations in which all disks and controllers or adapters are of the same type.

You select a disk type by clicking the arrows at the right of the list box until the desired disk type is displayed in the box, and then clicking the name of the disk type.

The list of disk types displayed is determined by the selected subsystem (controller or adapter) type, so it makes sense to select the subsystem type first, and then choose the disk type from the resulting list.


Disk MTTR

Use this field to specify the disk MTTR for Mean Time Between Data Loss (due to disk failure) calculations. Array reliability calculations require both MTBF and MTTR for a single disk as input. MTBF data for Digital's major disk products is built into the program. MTTR is primarily a function of installation policy and practice, so it is left for the user to supply.

The default value of 24 hours represents an average case. By dedicating a spare disk for replacement of a failed array member disk, MTTR can be shortened to the time required to reconstruct the contents of the failed disk. (This time must always be counted, since the array is not restored to high-availability state until its capability to store redundant data is fully operational.)


AvgReadSize
Average Read Size (KBytes)

Use this field to specify the average size of a read request for the active Workload in KBytes (1 KByte = 1024 bytes). The RAID Evaluator program only models I/O profiles at the average parameter level.


AvgWriteSize
Average Write Size (KBytes)

Use this field to specify the average size of a write request for the active Workload in KBytes (1 KByte =1024 bytes). The RAID Evaluator program only models I/O profiles at the average parameter level.


ReadPercentage
% Reads

Use this field to specify the read/write mix for the active Workload. You specify the percentage of the Workload's total requests that are reads; the remainder are assumed to be writes.

The read/write mix can have a significant effect on performance, especially with RAID Levels 3 and 5.


SeekPercentage
Locality of Reference

Use this field to specify the active Workload's locality of reference, or degree to which consecutive accesses to a disk reference adjacent data. You specify this parameter as a fraction of the disk's average seek time.

If a Workload is known to make heavy reference to a few relatively small files, this parameter should be set to a low value (10% or less).

The default of 40% represents an average value that has been observed by Digital to be representative of several multi-user workloads.

If you feel that evenly distributed seeking across disks' entire surfaces is characteristic of the Workload you are modeling, specify this parameter as 100%. This represents evenly distributed seeks across the entire disk for each disk in the Workload.


ResponseTime
Req'd Response Time (ms)

Use this field to specify the required response time for the active Workload when the active Workload has been specified as thruput-intensive. (This field has no effect, and is greyed so that you cannot enter data in it, when a bandwidth-intensive Workload is active.)

The response time of an I/O configuration can vary considerably as a function of the degree to which the configuration's resources are saturated. When the number of requests arriving at the configuration is close to its request processing capability, queueing occurs, and response times rise considerably. This is usually intolerable from a user or application standpoint, so the program gives you the capability to specify an average response time requirement for thruput-intensive Workloads. All performance calculations are based on the ability to deliver this response time rather than the configuration's ability to process requests.

The effect of request arrival rate on response time can be seen dramatically in the Curves window, where response time is plotted as a function of request arrival rate. These curves are always "knee-shaped", with response time rising asymptotically to an infinite value at an average request rate that represents the configuration's physical ability to handle requests (its saturation point).


ComputeNow
Compute C-A-P

Click this button to compute the C-A-P Analysis for the active Workload. If a C-A-P Analysis window exists for the active Workload, it is updated to reflect the results based on any parameter changes made in the Input panel . Likewise, if a Bar Graph or Curve window for the active Workload exists, it is updated. If a Comparison window exists, the affected Workload's curve in it is updated as well.

If no C-A-P Analysis window exists for the current Workload, one is created, provided that the limit of four simultaneous C-A-P Analysis windows has not been reached.


CtlrType
Subsys Type

Use this field to specify the controller or adapter type for the active Workload. The current version of the RAID Evaluator program only supports homogeneous configurations, i.e., configurations in which all disks and controllers or adapters are of the same type.

You select a subsystem type by clicking the arrows at the right of the list box until the desired subsystem type is displayed in the box, and then clicking its name.

The list of disk types displayed is determined by the selected subsystem, so it makes sense to select the subsystem first, and then choose the disk type from the resulting list.


ArrayCount
# of Arrays (Proposed or Selected)

Use this field to specify the number of RAID 3 and RAID 5 arrays to be used in C-A-P Analysis calculations. Each time you redefine the number of disks (by choosing a disk type, or specifying a required capacity or utilization percentage), The program proposes a number of arrays in this box. The number is chosen so that the size of an array is as close to 6 as possible.

You may override this proposal by entering an alternative number in the edit box. You must enter a submultiple of the number of disks shown directly above. For example, with a configuration that implies 12 disks, you may specify 1, 2, 3, 4, or 6 arrays, but not 5, 7, or any other number.

The label to the left of this field changes to tell you whether the current number of arrays is the number proposed by program or an alternative selected by you.

This field is not persistent. Each time a Workload is reactivated, the program re-proposes a number of arrays. This will be changed in a future version.


BWIntensive
Bandwidth Intensive (Radio Button)

Click this button to specify that the active Workload is to be regarded as bandwidth-intensive. This causes the program to use different algorithms in its performance calculations. These algorithms assume a continuous supply of I/O requests to each disk in the configuration. This makes the Req'd Response Time and the load imbalance parameters irrelevant, so these are greyed in the Input panel  when this button is set. Values stored in them prior to checking the Bandwidth Intensive button are saved, however, and are used in the event that the Workload is ever specified to be thruput-intensive.


TPIntensive
Thruput Intensive (Radio Button)

Click this button to specify that the active Workload is to be regarded as thruput-intensive. This is the default condition when the program creates new Workloads. A thruput-intensive Workload is one that must meet an average response time criterion (which you specify).

Calculations for thruput-intensive Workloads also assume that there is some imbalance among the disks in the configuration, i.e., that some fraction of the disks receives a disproportionate share of the I/O requests. You specify this imbalance using the two edit boxes labeled % of I/O goes to and % of Storage in the Input panel .

Note:	the RAID Evaluator program's algorithms assume that imbalance persists, even when storage is arrayed. Thus, if you specify that 80% goes to 20% of the storage in the configuration, the performance calculations for RAID 0, RAID 3, and RAID 5 all assume that 80% of the I/O goes to 20% of the arrays. Within each array, load balancing consistent with the array model is assumed.


PercentOfDisks
% of I/O (goes to % of Storage)

Use this field in conjunction with the % of Storage field to specify I/O imbalance for thruput-intensive Workloads. It specifies the share of the Workload's total I/O requests per unit time that are directed at the configuration's busiest disks.

This parameter is not relevant for bandwidth-intensive Workloads, so while the Bandwidth-intensive radio button is selected, this box is greyed. If you have previously supplied a value for this parameter, it is stored in the Workload's memory image, and is written to disk any time you save the Workloads in memory in a file, whether or not the Workload is specified as thruput-intensive at the time of saving.


PercentOfWork
(% of I/O goes to) % of Storage

Use this field in conjunction with the % of I/O goes to field to specify I/O imbalance for thruput-intensive Workloads. It specifies the share of the share of the configuration's disks to which the bulk of the Workload's I/O requests are directed.

This parameter is not relevant for bandwidth-intensive Workloads, so while the Bandwidth-intensive radio button is selected, this box is greyed. If you have previously supplied a value for this parameter, it is stored in the Workload's memory image, and is written to disk any time you save the Workloads in memory in a file, whether or not the Workload is specified as thruput-intensive at the time of saving.


RegenMode
RAID5 Regen Mode (Check Box)

Check this box to model the performance of a RAID5 array in reduced mode, i.e., while it is missing a disk, and must therefore regenerate any requests that involve the missing disk.

The RAID Evaluator only models a single array in reduced mode, so you cannot check this box if the Number of Arrays box indicates other than one array.


LoadFactor
Disk Utilization (%)

Use this field to specify a disk utilization factor. Installations very often limit the percentage of a disk's total storage capacity that they will allow to be occupied by data on a steady-state basis. They do this partly for performance reasons, but more important, to avoid job failures due to failure to allocate space for needed files because the designated disk was full.

This parameter gives you a way to input this condition to the program's modeling process if it is relevant for you. If you wish to ignore this facility, specify 100 as the percentage utilization.


Graph Button

Clicking this button causes a Bar Graph windows to be displayed. Each C-A-P Analysis window contains a Graph Button. The Bar Graph window displayed when this button is clicked displays a graphical representation of the data contained in the corresponding C-A-P Analysis window.

When you update a Workload's parameters and recompute the C-A-P analysis, any existing Bar Graph window is automatically updated.

The Bar Graph window is a child of the C-A-P Analysis window from which it is created. When you close its parent, the Bar Graph window closes as well.


Curve Button

Clicking this button causes a Request/Response Curve window to be displayed. Each C-A-P Analysis window contains a Curve Button. The Request/Response Curve window displayed when this button is clicked displays a graph of response time as a function of request arrival rate for the Workload data contained in the corresponding C-A-P Analysis window.

When you update a Workload's parameters and recompute the C-A-P analysis, any existing Request/Response Curve window is automatically updated. With slower personal computers, this can take as much as 5-8 seconds.

The Request/Response Curve window is a child of the C-A-P Analysis window from which it is created. When you close its parent, the Request/Response Curve window closes as well.


Write Button

Clicking this button causes the current contents of the C-A-P Analysis window to be written to a Result Text file file. A Result Text file can be printed or manipulated by a text editor.


Close Button

Clicking this button causes the C-A-P Analysis window to close. When you close a C-A-P Analysis window, its associated Bar Graph windows and Request/Response Curve window (if any) close as well.


Data Buttons

These buttons control which of three types of data from the C-A-P Analysis window are displayed in the Bar Graph windows in which they appear. The Bar Graph window can display one type of data at a time.

Clicking the Rqst Rate button causes Thruput, or number of I/O requests per second at the specified average response time, to be displayed.


ExpZoomButtons
Expand and Zoom Buttons

Clicking this button causes the vertical scale for the curves in the Request/Response Curve window to be expanded or contracted. In Zoom mode, the height of the vertical scale is limited to approximately four times the value of the Workload's specified required response time. In Expand mode, the height of the vertical scale is approximately ten times the value of the required response time.


CurveOnOffButtons
Curve Control Buttons

These buttons in the Request/Response Curve window cause individual curves to be displayed or suppressed. Each time a curve is added to or removed from the display in this window, the curves are replotted using a new scale to maximize the detail shown. To see more detail in the Independent Disks or RAID Level 3 cases, higher-performing options, such as RAID 0+1 and RAID 5 (in some cases) can be suppressed by clicking their respective buttons.


Bitmaps by Reference

A bitmap can be placed in a sentence [image], just like any character. Click on the maximize button bitmap to open a pop-up box with more information.

You can also put bitmaps at the left margin of the Help window. Text will automatically wrap along the right edge of the bitmap.

Or the bitmap can be at the right window margin, and text will automatically wrap along its left edge.


The coding for this bitmap is:

text...text...

Note: You cannot code bml or bmr bitmaps

as hotspots in this version of Help.


Visually Placed Bitmap

The Microsoft logo shown here was pasted from Clipboard into the Help topic file using Word for Windows.

Try clicking on the logo.


The Microsoft logo is a registered trademark of Microsoft Corporation.


Windows System Fonts

This is Courier 10 point.

This is Helv 10 point.

This is Modern 12 point.

This is Roman 12 point.

This is TMS RMN 12 point.


Note: 	Although they are available in Windows,

the Script and Symbol fonts do not display

with this version of Help shipped with the 3.0 SDK.

This is Script 12 point.

Τηισ ισ Σψμβολ 12 ποιντ (Symbol font).


Vowels and Consonants

Find the vowels and consonants in the word below by clicking on them one at a time.

Microsoft


The letter M is a consonant.


Yes, the letter i is a vowel.


No, the letter c is not a vowel.


R is a consonant.


This letter o is one of two in the word Microsoft.


The letter s is between two vowels in this word.


This o is the second one in Microsoft. Did you find the other one?


No, f is not a vowel.


The trailing t in Microsoft is a consonant.


Tutorial Lesson

There are three things to remember about your life vest:


Tutorial Lesson

There are three things to remember about your life vest:

Where it is.


Tutorial Lesson

There are three things to remember about your life vest:

Where it is.

How to put it on.


Tutorial Lesson

There are three things to remember about your life vest:

Where it is.

How to put it on.

How to inflate it.


Help can be authored with interactive instructional segments:


Congratulations!

You have found a topic that has no context-string identifier. It is accessible from a browse sequence only.

Can you think of a reason to author such a topic?


Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

WinHelp

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Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

WinHelp

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Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

WinHelp

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Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

WinHelp

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Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

WinHelp

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Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

WinHelp

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Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

WinHelp

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Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

WinHelp

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Simulation

Help can be used for simple simulations.

Click the check boxes in any order to change the format of the word WinHelp below:

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Eureka!

You found a topic that is accessible from a keyword search only. This topic is not linked through hypertext in any way.

You can use this technique to access topics without having to index them and author jumps. You can also access topics like this directly from your application through the use of multiple keyword tables.


Windows Keys

The keyboard topics below come from Help for Windows. You can create similar keyboard topics for your application's Help. Choose from the following list to review the keys used in Windows:

Cursor Movement Keys

Dialog Box Keys

Editing Keys

Help Keys

Menu Keys

System Keys

Text Selection Keys

Window Keys


Cursor Movement Keys

Key(s)	Function

DIRECTION key	Moves the cursor left, right, up, or down in a field.

End or Ctrl+Right Arrow	Moves to the end of a field.

Home or CTRL+Left Arrow	Moves to the beginning of a field.

PAGE UP or PAGE DOWN	Moves up or down in a field, one screen at a time.


Dialog Box Keys

Key(s)	Function

TAB	Moves the focus from field to field in the forward direction. Edits you have made to an input field take effect when you use TAB or the mouse to move the focus to another field.

SHIFT+TAB	Moves the focus from field to field in reverse direction. Edits you have made to an input field take effect when you use TAB or the mouse to move the focus to another field.

ALT+letter	Moves to the option or group whose underlined letter matches the one you type.

DIRECTION key	Moves from option to option within a group of options, or from character to character if the focus is within an edit field.

ENTER	If the focus is on a button: executes the command  on the button.
If the focus is not on a button: has no effect. ENTER does not have any effect on edit fields.

ESC	Closes a dialog box without completing the command. (Same as Cancel)

ALT+DOWN ARROW	When the focus is on the Workload Name edit field:toggles the drop-down list box of Workload names open and closed.
Otherwise: No effect.

ALT+UP or DOWN ARROW	Selects item in a drop-down list box.

SPACEBAR	When focus is on an edit box: inserts a space in the input.
Otherwise: no effect.

When focus is on the RAID5 Regen Mode checkbox:Sets or clears the check in the check box.

CTRL+SLASH	Selects all the items in a list box.

CTRL+BACKSLASH	Cancels all selections except the current selection.

SHIFT+ DIRECTION key	Extends selection in a text box.

SHIFT+ HOME	When the focus is on an edit box (including the Workload Name edit box): Extends selection to first character in the edit box.
When the focus is on a list box (i.e., the Subsys Model, Disk Model, or Workload Name list boxes): Selects the first item in the list box.

SHIFT+ END	Extends selection to last character in an edit box


Editing Keys

Key(s)	Function

Backspace	Deletes the character to the left of the cursor.

Or, deletes selected text.

Delete	Deletes the character to the right of the cursor.

Or, deletes selected text.


Help Keys

Key(s)	Function

F1	Gets Help and displays the Help Index for the application. If the Help window is already open, pressing F1 displays the "Using Windows Help" topics.

In some Windows applications, pressing F1 displays a Help topic on the selected command, dialog box option, or system message.

SHIFT+F1	Changes the pointer to [image] so you can get Help on a specific command, screen region, or key. You can then choose a command, click the screen region, or press a key or key combination you want to know more about.

(This feature is not available in all Windows applications.)


Menu Keys

Key(s)	Function

Alt	Selects the first menu on the menu bar.

Letter key	Chooses the menu, or menu item, whose underlined letter matches the one you type.

Alt+letter key	Pulls down the menu whose underlined letter matches the one you type.

LEFT or RIGHT ARROW	Moves among menus.

UP or DOWN ARROW	Moves among menu items.

Enter	Chooses the selected menu item.


System Keys

The following keys can be used from any window, regardless of the application you are using.

Key(s)	Function

Ctrl+Esc	Switches to the Task List.

Alt+Esc	Switches to the next application window or minimized icon, including full-screen programs.

Alt+TAB	Switches to the next application window, restoring applications that are running as icons.

Alt+PrtSc	Copies the entire screen to Clipboard.

Ctrl+F4	Closes the active window.

F1	Gets Help and displays the Help Index for the application. (See Help Keys)


Text Selection Keys

Key(s)	Function

SHIFT+LEFT or RIGHT ARROW	Selects text one character at a time to the left or right.

SHIFT+DOWN or UP	Selects one line of text up or down.

SHIFT+END	Selects text to the end of the line.

SHIFT+HOME	Selects text to the beginning of the line.

SHIFT+PAGE DOWN	Selects text down one window.

Or, cancels the selection if the next window is already selected.

SHIFT+PAGE UP	Selects text up one window.

Or, cancels the selection if the previous window is already selected.

CTRL+SHIFT+LEFT or RIGHT ARROW	Selects text to the next or previous word.

CTRL+SHIFT+UP or DOWN ARROW	Selects text to the beginning (UP ARROW) or end (DOWN ARROW) of the paragraph.

CTRL+SHIFT+END	Selects text to the end of the document.

CTRL+SHIFT+HOME	Selects text to the beginning of the document.


Window Keys

Key(s)	Function

ALT+SPACEBAR	Opens the Control menu for an application window.

ALT+Hyphen	Opens the Control menu for a document window.

Alt+F4	Closes a window.

Alt+Esc	Switches to the next application window or minimized icon, including full-screen programs.

Alt+TAB	Switches to the next application window, restoring applications that are running as icons.

Alt+ENTER	Switches a non-Windows application between running in a window and running full screen.

DIRECTION key	Moves a window when you have chosen Move from the Control menu.

Or, changes the size of a window when you have chosen Size from the Control menu.


$ Dummy
   DUMMY

A Dummy fills space.


Adapter

An adapter is a hardware component that connects storage elements or storage subsystems to a host computer's memory bus. Adapters do not generally provide low-level disk control functions, but do provide the path over which high-level commands and responses are communicated between host and storage element or subsystem. Adapters also provide the path over which data moves between host computer memory and storage.

The CIXCD, CIBCA, CI780, KFMSA, and KFQSA are examples of storage adapters from the Digital product line. Some of Digital's older storage controllers, for example, the KDA50 and the KDM70 have the adapter component built into the disk controller.

cf. Controller


Array

An array is a collection of disks, controller and adapter hardware as required to make them function, and software that makes them appear to host file systems and applications as if they were a single disk.

The software component of an array performs I/O scheduling and redirection and data mapping functions. It may reside either in the host computer (host-based RAID, or HBR) or in a controller (subsystem-based RAID, or SBR).


Bar Graph Window

A Bar Graph window shows the performance or data reliability information from a C-A-P Analysis windows in bar graph form. It conveys no additional information, but the graphical format can help you visualize the relative performance and data reliability properties of the different RAID models.

You create a Bar Graph window by clicking the Graph button in a C-A-P Analysis window. A Bar Graph window displays data from the C-A-P Analysis window from which it was spawned. When you update a C-A-P Analysis (by activating the corresponding Workload , changing one or more of its parameters, and clicking the Compute C-A-P button in the Input panel , the corresponding Bar Graph window is updated as well.

A Bar Graph window displays one output parameter at a time. You select which output to display by clicking one of three buttons:

Click the Rqst. Rate button to display relative request rates for each of the supported RAID models at the specified thruput.

Note: Some RAID models are not computed when you specify a Bandwidth-intensive Workload. These display as bars of zero height in the Bar Graph window.

Click the Bandwidth button to display the bandwidth that corresponds to the request rate at the specified thruput.

Click the Data Rel. button to display the relative data reliability of the RAID models supported by the RAID Evaluator program.

The Bar Graph window also contains a Close button. When you close a Bar Graph window this way, there is no effect on any other RAID Evaluator child window. When you close the parent C-A-P Analysis window, the Bar Graph window closes as well. When you use the Close Bar Graph Windows command on the Windows menu, all Bar Graph windows close, but no other output windows are affected.


Built-in Controller

A Built-in Controller is a controller whose parameters are coded into the RAID Evaluator program and cannot be changed by the user through the Controller Definition dialog box.

The RAID Evaluator program also supports User-Defined Controllers and User-Defined Disks, whose parameters can be changed by the user through the Controller Definition dialog box and Disk Definition Dialog box respectively.


Built-in Disk

A Built-in Disk is a disk whose parameters are coded into the RAID Evaluator program and cannot be changed by the user through the Disk Definition dialog box.

The RAID Evaluator also supports User-Defined Controllers and User-Defined Disks, whose parameters can be changed by the user through the Controller Definition dialog box and Disk Definition Dialog box respectively.


C-A-P Analysis

A C-A-P (Cost-Availability-Performance) Analysis is the program's basic output. It appears in the C-A-P Analysis window, and shows:

relative cost (measured in subsystems and drives),

availability (measured relative to that of a single disk), and,

performance (measured in requests per second for thruput-intensive Workloads and in MBytes per second for bandwidth-intensive Workloads).

for a Workload.


C-A-P Analysis Window

A C-A-P (Cost-Availability-Performance) Analysis is the RAID Evaluator program's fundamental output. It compares relative cost (measured in subsystems and drives), availability (measured relative to that of a single disk) and performance (measured in requests per second for thruput-intensive Workloads  and in MBytes per second for bandwidth-intensive Workloads) for a single Workload.

The contents of a C-A-P Analysis window may be printed in a Result Text File if one is active by clicking the  button.

A C-A-P Analysis window contains four buttons.

1.	Click the Close button to close the C-A-P Analysis window (and its child  and Request/Response curve windows if you have created them).

2.	Click the Write button to write the contents of the C-A-P Analysis window to a Result Text file if one is active.

3.	Click the Graph button to display selected data from the C-A-P analysis window in bar graph form in a Bar Graph windows.

4.	Click the Curve button to display Request/Response curves for each RAID model for the given Workload in a Request/Response Curve window.


Configuration Comparison Window

The Configuration Comparison window allows you to compare the effect that differences in hardware configuration or I/O profile have on a single RAID model. When you create it (by clicking the Compare Displayed Curves command on the Windows menu or the Comparison button on the ), the Configuration Comparison window displays the Independent Disk Request/Response curves for each existing Request/Response curve window on a single scale.

Eight radio buttons give you the option of displaying comparative Request/Response curves for any single RAID model. The radio button labeled Single Disk is only enabled for Bandwidth-intensive Workloads. When the Single Disk button is enabled, the button labeled Ind. Disks is disabled. Similarly, the button labeled RAID5 Regen is only enabled when the Workload is defined so that reduced RAID5 mode is in effect (RAID5 with one disk missing from the array).

A Configuration Comparison window contains two buttons.

Click the Close button to close the Configuration Comparison window.

Click the Expand button (same as the Zoom button) to expand the range of the vertical axis so that the asymptotes of the displayed curves are more nearly shown.

Click the Zoom button (same as the Expand button) to contract the range of the vertical axis so that more detail is shown in the region of the curves' knees.

You can resize or minimize the Configuration Comparison window. It closes automatically when there are no longer any Request/Response curve windows.


$ Controller
Controller

A controller is a hardware component of a storage subsystem which provides high-level to low-level translation of commands issued to one or more disks by a host, and manages the flow of data and messages between disks and the adapter which provides access to host memory.

Controllers are required when the disk or storage element does not include sufficient intelligence to communicate directly with a host adapter.

The HSC40-50-60-65-70-90-95 family, the KDM70, and the UDA50-KDA50-KDB50 family are examples of storage controllers from the Digital product line.


$ Controller Definition dialog box
Controller Definition dialog box

A Microsoft Windows dialog box used to define the parameter values for controllers, or to alter the parameter values for already-defined controllers.

In order for the RAID Evaluator program to use a User-Defined Controller in C-A-P Analyses, the following parameters must be supplied for it:

Name	An arbitrary character string of up to 15 bytes which appears in the Subsystem Type list box in the Workload Description dialog box.

Bus	An arbitrary character string of up to 15 bytes which is used to match controllers with drives eligible to be attached to them.

Disks Supported	The maximum number of disks that can be attached to the controller.

Transfer Rate	The maximum rate at which the controller can transfer data to or from hosts. (the program assumes that controller-to-host transfer rate is the same for reading and writing). This number must be supplied in MBytes/second. (e.g., a maximum transfer rate of 500 KBytes/second would be input as 0.5.)

I/O Rate	The maximum number of 4 KByte I/O requests that the controller can process in a second. (The RAID Evaluator program assumes that controller processing overhead for read and write requests is the same.)


$ Data Reliability
Data Reliability

In the RAID Evaluator context, data reliability refers to the ability of a body of data stored on disks to resist destruction due to disk failure. The program only models the effect of disk failure on data reliability. Other factors, notably application failures, can also affect the reliability of data.

The RAID Evaluator program models data reliability for the purpose of comparing different RAID models with each other. To simplify analysis, relative data reliability is reported, with the reliability (MTBF) of a single disk taken as unity. While this is arguably biased (because an application which stores its data on independent disks may in fact continue to provide a significant share of its function in the event of certain disk failures), it is difficult to generalize any other model.


$ Disk
Disk

Disk Drive

A disk or disk drive is a block-addressable non-volatile mass storage device. When the unqualified term disk is used in the RAID Evaluator context, a physical disk is meant.

cf. Virtual disk


$ Disk Definition dialog box
Disk Definition dialog box

A Microsoft Windows dialog box used to define the parameter values for disks, or to alter the parameter values for already-defined disks.

In order for the RAID Evaluator program to use a User-Defined Disk in C-A-P Analyses, the following parameters must be supplied for it:

Disk Name	An arbitrary character string of up to 15 bytes which appears in the Disk Type list box in the Workload Description dialog box.

Controller Bus	An arbitrary character string of up to 15 bytes which is used to match controllers with disks eligible to be attached to them.

Rotation Speed	The RPM at which the disk spins. Used in rotational latency and on-track data transfer speed calculations.

Spiral Data Transfer Rate	The rate as which the disk will satisfy the data transfer portion of a long (multi-track) data transfer request.

Read Seek Time	The average seek time for read requests.

Write Seek Time	The average seek time for write requests. (For certain disk models, the read and write seek times differ).

Disk Capacity	This is the net usable capacity of the disk. This is used in calculating the number of disks required to satisfy a given workload. Expressed in MBytes (e.g., a 2 GByte disk would be described by the value 2000.0).

Track Capacity	The amount of user data stored on each track of the disk. For banded (zone-bit-recorded) disks, an average value should be used. Note that this is expressed in 512-byte blocks.

Single-Disk MTBF	The mean time before failure for a single disk of this type. Expressed in hours. This is used in array MTDL calculations.


Independent Disks

The term independent disks is used to describe disks that are not aggregated into an array. This is the conventional way of managing multiple disks in computer installations today. It contrasts with arrays, in which several disks are managed and presented to the host as if they were one.

For thruput-intensive Workloads, the RAID Evaluator program uses independent disks as the base point against which to compare other RAID models in cost, availability, and performance.

For bandwidth-intensive Workloads, the program uses a single disk as the main point of comparision, since bandwidth-intensive Workloads typically represent single-stream I/O, which in the absence of an array would have to be delivered by a single disk.


Input panel

The Input panel is a Microsoft Windows dialog box that resides permanently in the main window. It is divided into left-hand and right-hand sides for data input, and includes four buttons you can use to cause actions.

You use the left-hand side of the Input panel to specify information about the subsystem hardware configuration.

You use the right-hand side of the Input panel to specify information about the application I/O profile you are modeling.

You can move the Input panel around within the main window, but you cannot resize it, close it, or shrink it to an icon.


Load Balance
I/O Load Balance

I/O Load Balance refers to the fraction of the Workload's total requests directed at the busiest disks in the Workload.

You specify the I/O Load Balance by specifying the percentage of requests comprising the majority of the Workload and the percentage of disks or arrays in the Workload to which they are directed. For example, you might specify that 80% of the I/O requests in the Workload are to be directed to 20% of the disks or arrays in the configuration.

You must specify the I/O Load Balance so that the percentage of requests is at least as great as the percentage of storage at which they are directed (e.g., 80% if the I/O requests directed to 30% of the disks ratherthan the reverse). If you do not, the program informs you with a message box that it is complementing the values.

To specify an evenly balanced Workload, use the same value for percentage of I/O requests and percentage of storage.  Any valid value may be used (e.g., 50% of I/O requests directed to 50% of storage).


I/O Profile

A RAID Evaluator I/O Profile consists of average read and write sizes, a locality of reference (seek range) specification, and a specification of whether the I/O profile is bandwidth-intensive or thruput-intensive.

For thruput-intensive I/O profiles, a response time requirement and a read/write balance must also be specified.

The I/O profile appears on the right-hand side of the RAID Evaluator Input panel.


Locality of Reference

The Locality of Reference parameter in the Input panel gives you a means of specifying average seek distance for a Workload. You specify Locality of Reference as a percentage of a disk's average hardware seek time.

The default Locality of Reference parameter built into the program is 40% of a disk's average seek time. This approximates many VMS multi-user I/O profiles.

To specify a uniform distribution of seeks across the entire surface of all disks, enter a value of 100% in the Locality of Reference box in the Input panel.


RAID

RAID Level

RAID stands for Redundant Array of Independent Disks. The term was coined by researchers at the University of California at Berkeley in 1987 in their search for lower cost highly reliable alternatives to the large relatively expensive disk drives of that time.

RAID is a family of techniques for using multiple disk drives as arrays. Each technique in the family has different net cost, availability, and performance (C-A-P) properties.

The Berkeley researchers identified five RAID techniques, which they named Levels 1 through 5. The levels are usually referred to by the names RAID 1, RAID 2, RAID 3, RAID 4, and RAID 5. Common industry practice has since added a sixth Level, RAID 0, and a seventh, RAID 6, although the latter is not widely implemented. A RAID 7 has been discussed, but there is not general agreement on its definition.

Since all three measures of RAID (cost, availability, and performance) do not all increase in goodness with higher RAID Level numbers, the RAID Levels do not form a hierarchy. It is more accurate to view them as occupying different points in a 3-dimensional mass storage quality space.


RAID 0

RAID 0 is also known as disk striping. Strictly speaking, it is not RAID at all, since no redundancy is provided. Its data mapping technique, however, is similar to RAID mapping, and so the term RAID 0 has come into use to describe it.

When disks are arranged in a RAID 0 array, consecutive data addresses seen by the host are mapped to the disks of the array in a round-robin fashion. The unit of physically contiguous data is known as a chunk.

For example, if the chunk for a 3-disk RAID 0 array were 50 blocks, then:

array blocks 1-50 would reside on disk 1

array blocks 51-100 would reside on disk 2

array blocks 101-150 would reside on disk 3

array blocks 151-200 would reside on disk 1

array blocks 201-250 would reside on disk 2

...and so on.

RAID 0 usually provides excellent performance for both thruput-intensive and bandwidth-intensive applications.

For thruput-intensive applications, the mapping of array blocks to physical disk blocks provides an even distribution of randomly addressed I/O requests across the disks in the array, so that if an I/O queue to the array exists, the chances are very high that multiple disks will be serving the queue concurrently. This can be seen with just about any Workload for which I/O imbalance exists by comparing the C-A-P Analysis performance for Independent Disks with that for RAID 0. For perfectly balanced Workloads, the two will be nearly identical.

For bandwidth-intensive applications, as long as the application makes large I/O requests, each request will tend to be served by multiple array members. (In the example above, a request for 150 blocks would have to be served by all three members). This reduces the data transfer portion of the I/O operation. The larger the I/O request, the greater the reduction.

RAID 0 does not enhance availability. In fact, it arguably reduces availability compared to independent disks, because if a single array member fails, it is extremely difficult to retrieve any data from the array. The program does not take this approach. It assumes that if a single independent disk fails, the subsystem is non-functional, and makes its relative data reliability calculations on that basis.

Digital's implementations of RAID 0 can both be used in conjunction with RAID 1 implementations to create striped arrays whose members are shadow sets. This combination has the same hardware cost as shadowing (RAID 1) alone, and provides the data reliability benefits of RAID 1 along with the performance benefits of RAID 0.


RAID 1

RAID 1 is also known as disk shadowing. Each array consists of two disks (for extremely high redundancy, 3-disk arrays are possible) on which identical data is stored.

The cost of RAID 1 is high -- each disk and port required by applications must be duplicated.

The availability of RAID 1 is also extremely high -- normally in the range of millions to tens of millions of hours mean time between data loss.

For thruput-intensive applications, the performance of RAID 1 is high compared to that of a single disk. For each read request, there are two servers (the two disks in the array). Thus, when load is heavy and queues build, RAID 1 arrays can support more I/O before reaching the knee of the Request/Response curve.

Writes to RAID 1 arrays exact a performance penalty -- both disks in the array must be written -- but the writes can be done concurrently, so the response time penalty is minimal. A RAID 1 array will saturate at a lower level than a single disk for write-intensive applications, however. This can be observed by constructing the appropriate Workloads.

The performance of RAID 1 can be substantially enhanced by the addition of RAID 0. While RAID 1 is an expensive storage solution compared to other RAID alternatives, the incremental cost of adding RAID 0 to a collection of RAID 1 arrays is low, and the potential performance gains are very high.

Compare RAID 1 with:

RAID 3 and RAID 5, which offer significantly higher data reliability than independent disks at lower cost than RAID 1, but whose performance is application dependent.

RAID 0+1, which offers significantly higher performance than RAID 1 alone at no incremental hardware cost.


RAID 3

Two important properties define a RAID 3 array:

its data is striped across all but 1 of its member disks with a very small chunk (typically less than a single block)

the remaining member stores redundant information, usually computed using an exclusive or function, about corresponding chunks stored on the other members.

The smallest atomic read or write operation on a RAID 3 array completely reads or overwrites a single corresponding chunk on each member. Every read or write to a RAID 3 array accesses or modifies corresponding chunks on all array members completely.

This property makes RAID 3 performance symmetric, i.e., it is the same for reading as for writing. RAID 3 arrays are therefore typically high performers in bandwidth-intensive applications.

On the other hand, since all the disks in a RAID 3 array operate in unison (in some implementations, they are even physically synchronized!), the array behaves approximately like a single disk for thruput-intensive applications, making them an ineffective solution.

RAID 3 should be carefully contrasted with RAID 5.


RAID 5

A RAID 5 array spreads data across all of the disks in the array in an arrangement similar to that used by striping. For an n-disk array, however, every nth chunk represents redundant information about the data stored in the corresponding n-1 chunks. This redundant information is distributed across the disks in the array to avoid hot spots (disproportionately busy disks) while updating.

Unlike RAID 3 arrays, the disks in a RAID 5 array are not synchronized. Moreover, chunks are made up of multiples of a disk block, usually on the order of the number of blocks in a track or more. As a result, most I/O requests to a RAID 5 array are satisfied by physical I/O to a single chunk.

For read access, this means that RAID 5 performance is similar to that of RAID 0. For a given user capacity and a given disk type, RAID 5 read performance will often be greater than that of RAID 0 because one more physical disk is required to realize an array of a given usable storage capacity.

For write access, however, data and parity must be updated as separate physical operations. This entails both reading and writing both the chunk to be modified and the corresponding parity chunk in order to satisfy a single write request to the array virtual disk. As a result, RAID 5 performance can be quite poor for applications in which write requests predominate in the physical I/O profile.

Compare RAID 5 with:

RAID 3, which offers superior bandwidth for bandwidth-intensive applications, but significantly inferior thruput (ability to satisfy large numbers of I/O requests per second) for thruput-intensive applications.

RAID 0+1, which offers superior performance and data reliability, albeit at significantly higher cost.


RAID 0+1

RAID 0+1 is a combination of RAID 0 (disk striping) and RAID 1 (volume shadowing). It is usually implemented by creating a series of shadow sets, or 2-member RAID 1 arrays, and striping the resulting virtual disks.

RAID 0+1 provides the best combination of high performance and data availability of any of the supported RAID models. Its only drawback is cost. The hardware cost for RAID 0+1 is identical to that of RAID 1 (shadowing) alone, i.e. no extra disks or ports are required. For the minor additional cost of the software required to stripe the RAID 1 shadowsets, I/O load can be balanced, and performance can be increased dramatically. Any Workload with imbalance between the disks in its configuration will illustrate this.

RAID 3 and RAID 5 provide lower cost alternatives to RAID 0+1. With either of these RAID Levels:

cost is substantially lower,

data availability is lower, but still high,

performance is application-dependent.

RAID 3 and RAID 5 might be thought of as being an intermediate level in a data reliability hierarchy. For a lower cost that full RAID 1, high data reliability can be achieved, but at some potential cost in performance.


Read/Write Balance
Read/Write Balance (% Reads)

Read/Write Balance refers to the fraction of read requests in an I/O Profile (non-read requests are assumed to be write requests). The RAID Evaluator model applies the same Read/Write Balance to all disks in a Workload.

You specify a Workload's Read/Write Balance by entering the percentage of read requests in the box in the I/O Profile section of the Input panel. The read percentage must be a whole number between 0 and 100 inclusive.


Reconstruction

Reconstruction is the process by which a RAID 1, 3, or 5 array recovers from a disk failure by populating a replacement disk with the contents of the failed disk, which it obtains by reconstructing them from the remaining members of the array.

High-quality RAID implementations will support on-line reconstruction, meaning that reconstruction can occur while the array is still providing storage and I/O services to applications.

Frequency of reconstruction is an important parameter to consider when choosing a RAID implementation because even though continued application service is usually provided during reconstruction, the I/O bandwidth required for reconstruction is so great that application performance is typically significantly diminished.


Regeneration

Regeneration is the process by which a RAID 1, 3, or 5 array delivers data to applications when the disk containing that data is missing from the array (e.g., due to a failure). Data is regenerated by accessing redundant data from logically corresponding locations on the remaining array members and performing operations dictated by the RAID level to recreate data from the missing drive.

An array with a missing member which must regenerate some data requested from it is said to be operating in reduced mode. In reduced mode, I/O performance is usually diminished.


Request/Response Curve Window

A Request/Response Curve window displays average response time (the elapsed time for an average request in the Workload ) as a function of the request rate (number of requests arriving at the subsystem per second) for a Workload whose C-A-P Analysis is displayed in a C-A-P Analysis windows. Request/Response Curves can give you a feeling for how responsiveness of various RAID models degrades as the configurations become saturated with I/O requests.

You create a Request/Response Curve window by clicking the Curve button in a C-A-P Analysis window. The Request/Response Curve window displays data from the C-A-P Analysis window from which it was spawned. When you update a C-A-P Analysis (by making the corresponding Workload active, changing one or more of its parameters, and clicking the Compute C-A-P button in the Input panel , the corresponding Request/Response Curve window is updated as well.

Note: on slower personal computers, or personal computers without floating point hardware, the computation may require a few seconds.

You can control the RAID models for which Request/Response Curves are displayed by clicking check boxes at the top of the Request/Response Curve window. An x in a box means that the Request/Response curve for that RAID model will be displayed.

Hint: Each time a RAID model is added to or deleted from the display, the horizontal scale for plotting is recomputed. By deleting higher-performance RAID models from the display, you can see in greater detail how the lower-performance RAID models compare to each other.

In addition, you may:

Click the Expand button (same as the Zoom button) show an enlarged vertical scale. For most Workloads, the expanded Request/Response curve essentially shows the response time asymptote, and gives a very good idea of the request rate at which the Workload completely saturates each hardware configuration.

Click the Zoom button (same as the Expand button) to reduce the vertical scale so you can see more detail in response time regions of more practical interest.

Click the  Close button to close the Request/Response Curve window. When you close a Request/Response Curve window window this way, there is no effect on any other child window. When you close the parent C-A-P Analysis window, the Request/Response Curve window closes as well. When you use the Close Curves Windows command on the Windows menu, all Request/Response Curve windows close, but there is no effect on other windows.


Result Text File

A Result Text file is an ASCII text file into which the program will write a formatted version of the data displayed in a C-A-P Analysis window. A Result Text file can be manipulated using the Microsoft Windows Notepad tool, the MS-DOS V5.0 Editor, or any other text processor capable of handling text files.

You open a Result Text file by using the Open Result Text File... command on the File menu and specifying a pathname in the resulting file dialog. If you specify an existing Result Text file, any data you write is appended to the end of it. If you specify a nonexistent file, a dialog asks you to verify that you want to create a new Result Text file.

You write to a Result Text file by using the Write button in a C-A-P Analysis window.

You close a Result Text file by using the Close Result Text File command on the File menu. Closing a Result Text file disables further writing of C-A-P Analysis results in text form.

One Result Text file may be active at a time.

Note: The RAID Evaluator program checks the signature of the active Result Text file before writing data into it. The signature is a character string at the front of the file. If you expect to write more data into a Result Text file, do not change the signature at the front of the file while you are editing it.


Storage Element

A Storage Element is a disk drive with a built-in controller. It attaches directly to an adapter over an I/O bus.

The RF30, RF71, RF25, etc. are examples of storage elements from the Digital product family. Most SCSI-attached disk drives can be properly described as storage elements.


Subsystem

An I/O subsystem is a set of disks or storage elements and the controllers and/or adapters required to connect them to host computers.

The RAID Evaluator program models only homogeneous subsystems, that is, subsystems consisting entirely of a single type of disk and controller or adapter. In addition, only disks are modeled, except to the extent that the program includes sufficient controllers or adapters in its computed configurations to handle the bandwidth, I/O request rate, and disk connectivity required by each RAID model for the Workload being analyzed.

You define the subsystem part of a RAID Evaluator Workload using the left-hand side of the Input panel.


User-Defined Controller

A User-Defined Controller is one whose parameters are supplied to the program by the user through the Controller Definition dialog box. The program stores User-Defined Controller parameters in a database, so they need be defined only once. User-Defined Controller parameters may be modified at any time by using the Controller... command on the Parameters menu. Modifications to User-Defined Controller parameters do not take effect, however, until the program has been stopped and restarted.

Parameter values for some Digital-supplied disks and controllers are built into the program. These are referred to as Built-in Controllers and Built-in Disks respectively. The parameter values for these devices have been determined by actual experience, and cannot be altered by the user.


User-Defined Disk

A User-Defined Disk is one whose parameters are supplied to the program by the user through the Disk Definition dialog box. The program stores User Defined Disk parameters in a database, so they need be defined only once. User-Defined Disk parameters may be modified at any time by using the Drive... command on the Parameters menu. Modifications to User-Defined Disk parameters do not take effect, however, until the program has been stopped and restarted.

Parameter values for some Digital-supplied disks and controllers are built into the program. These are referred to as Built-in Controllers and Built-in Disks respectively. The parameter values for these devices have been determined by actual experience, and cannot be altered by the user.


Virtual Disk

A virtual disk is an abstract entity that exhibits the important properties of a disk to a computer system. The image presented by RAID software to host computer I/O and file system software is that of a virtual disk.

In the RAID Evaluator context, the terms virtual disk and array are often used interchangeably.


Workload

A RAID Evaluator Workload is a parametric description of an I/O hardware subsystem and an application I/O profile.

All the data that appears in the Input panel at one time comprises the active Workload.


Workload File

A RAID Evaluator Workload file is a collection of Workloads stored permanently on a disk (the program supports both hard disks and floppy disks as data storage media). When you open a Workload file using the Open Workload File... command, it becomes the active Workload file, and all the Workloads in it are read into memory.

One Workload file may be active at a time.

If you create one or more Workloads in memory (by editing the contents of the Input panel), and wish to save them in a file, use the Save Workload File As... command.

If a Workload file is active, and you wish to save the current contents of Workload memory in it, use the Save Workload File command. This command saves the current contents of Workload memory in the active Workload file. If you have modified the Workloads in memory since the active Workload file was last saved, a dialog will request that you confirm your desire to overwrite the Workload file on disk.