Setup / Configure RAID

The RAID Configuration Program Screens
When you configure your disk array, or even just view its configuration, you will be using the IBM RAID configuration program on the IBM SCSI-2 Fast/Wide Streaming-RAID Adapter/A Option Diskette (also called the IBM RAID controller diskette). The following figure is a compilation of many of the IBM RAID Controller Disk Array
Configuration (also called the IBM RAID configuration program) screens. The list below the figure gives explanations of the numbered areas of the figure.

1. This pop-up allows you to select the RAID level you want to assign to the logical drive you are defining, and it allows you to select the logical drive size. You can enter the size, in megabytes, or you can accept the default value shown. When you need to confirm an action, the Confirm pop-up appears in this area.
2. You can select any of the choices that appear on the menus.
3. The Bay/Array selection list shows each bay in the server (for each channel) numbered 1 through 7. The abbreviation in the bay indicates the status of the drive installed in the bay. Selections are made from this list
to determine which bays (hard disk drives) are in your arrays. The letter to the right of the bay, identifies the array in which the hard disk drive in that bay is grouped. Note: The Channel/Bay/Array area on the screen does not reflect the physical configuration of the server. In your server, the hard disk drives are installed in horizontal banks of bays (in banks C, D, and E there are 6 bays, numbered 1 through 6 from left to right). See Installing Internal Drives to see the physical location of the hard disk drives.
4. The Array list shows you the array ID and the size (in megabytes) of the array. Note: The capacity (size) is shown in binary equivalent. When a drive is being rebuilt, this area, along with the Logical Drive list area, shows the progression of the rebuilding process.
5. The Logical Drive list identifies the logical drive (for example, A1), the size of the logical drive, the RAID level assigned to the logical drive, the date it was created, and the write policy. The status of the logical drive also is shown. Good means that all is well with the drive; Critical means that you must replace the drive or do a rebuild operation. (You will have received a message telling you the drive is in a Critical state.) Offline means that the logical drive is nonrecoverable; the data in that drive is lost. When a drive is being rebuilt, this area, along with the Array list area, shows the progression of the rebuilding process. Note: The capacity (size) is shown in binary equivalent. During an initialization process, the Write Policy area displays the percent initialized; during a synchronization process, it displays the percent synchronized.
6. The information area tells you the action you can perform on this screen or pop-up.

Starting the RAID Configuration Program
   To start the RAID configuration program, insert the IBM RAID controller diskette into the primary drive and turn on the system. If the system already is on, press Ctrl+Alt+Del. If you have more than one RAID adapter, you will get an adapter selection screen. Otherwise, the Main Menu appears.
You can select Help from any menu. To return to the previous screen or to the previous work area of a screen,
press Esc. To select a menu item, press the number of the item or use the Up Arrow or Down Arrow to highlight the item, then press Enter.

The Main Menu contains the following choices:
o Help: Select this choice when you need additional information.
o View configuration: Select this choice to see the existing disk array configuration.
o Create/delete array: Select this choice to define a hot-spare drive, select the drives for an array you want to create, or to delete an existing array. This choice also has choices for defining a logical drive and formatting a drive. Whenever you make changes to the disk-array configuration and select Exit, the Confirm pop-up window will appear. You must select Yes to save and activate the changes. 
o Initialize/synchronize array: Select this choice after creating an array to:
- Set the drive to a predetermined value. For proper operation of RAID levels 1 or 5, you must select Initialize/synchronize array. Any data existing on the drive is overwritten with zeros, and the corresponding
parity information is initialized to the correct value.
You can choose to initialize more than one logical drive at a time. Also, you can interrupt the initialization process at any time by pressing Esc. Then, you can either restart the initialization process by pressing Enter,
or you can end the process by pressing Esc again.
- Synchronize logical drive: This selection recomputes and rewrites the parity data on the drive. You can select this choice to recompute parity data for RAID levels 1 or 5. This selection does not alter data on the drive. The synchronization process can be done on multiple logical drives.
o Rebuild device: Select this choice to rebuild logical drives. The rebuild operation is supported only for RAID levels 1 and 5.
o Advanced functions: Select this choice to change the write policy (the way data is written to the drive), to save your configuration information to a diskette, to restore it from a diskette, or to change RAID parameters. This choice also allows you to do a low-level format.
o Drive information: Select this choice to view information about the SCSI devices (hard disk, CD-ROM, tape, and so on) connected to the RAID adapter.
o Exit: Select this choice to leave the Main Menu.

Viewing the RAID Configuration
Before creating or changing a disk array, you can look at the current configuration by selecting View Configuration from the Main Menu of the RAID configuration program.
To view the disk-array configuration:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
2. Select View configuration. The current disk-array configuration information appears on the screen.
3. Press Enter to see the stripe order in the Bays Occupied (Ch:Bay) field.
4. Press any key to continue.
5. Press Esc to return to the Main Menu.

Performing Common Tasks
The Create/Delete Array menu of the RAID configuration program contains the more common tasks for configuring disk arrays. Procedures to complete these tasks are contained in the following subtopics.
Subtopics:
o Defining a Hot-Spare Drive
o Deleting a Disk Array
o Creating a Disk Array
o Adding Drives to Create an Additional Array
o Defining Logical Drives

Defining a Hot-Spare Drive
To define a drive as a hot-spare drive:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
2. Select Create/delete arrayfrom the Main Menu.
3. Select Define hot-spare drive.The cursor will become active in the Bay/Array selection list. Note: Only SCSI hard disk drives are shown as RDY, ONL, DDD, OFL, or HSP state. SCSI tape and
CD-ROM drives are not shown. They appear when you select drive information. Refer to Bay/Array Selection List for the drive status meanings. The numbers shown on the left are the bay IDs. See Installing Internal Drives for an explanation of the bay IDs.
4. Use the Up Arrow or Down Arrow to highlight the RDY (ready) drive you want to define as the hot spare; then press Enter. The RDY changes to HSP (hot spare). You can press Enter again to toggle between HSP and RDY.
5. Press Esc when you have finished. The cursor will become active in the Create/Delete Array menu.
6. If you want to create a disk array, go to Creating a Disk Array.
7. If you are finished:
a. Select Exit or press Esc. A pop-up window will appear asking you to confirm your change.
Note: The changes you make are not saved until you confirm them by selecting Yes in the Confirm pop-up window.
b. Select No if you do not want the drive you selected to be a hot spare; select Yes to define it as a hot-spare drive.
c. Back up the disk-array configuration information to diskette. Refer to Backing Up Your Disk-Array Configuration for instructions.

Deleting a Disk Array
The last array created must be the first deleted.
Warning:All the data and programs in the array are lost during this procedure. Before proceeding, back up any data and programs that you want to save. 
To delete a disk array:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
2. Select Create/delete arrayfrom the Main Menu.
3. Select Delete disk arrayfrom the Create/Delete Array menu. The cursor will be active in the Array list.
4. Review the Date Created column in the Logical Drive list; then press the Up Arrow or Down Arrow to highlight the most recently defined array. Warning:All the data and programs in the array will be lost during this procedure.
5. Press Del. The Confirm pop-up window appears.
6. If you do not want to delete the array, select No. To delete the array, select Yes. Note: To use hard disks from the existing array when creating a new array, you must confirm the deletion of the existing array.
If a defunct drive is still in a bay, the status shows a blank bay, as though there is no drive in that bay. When you replace the drive, the status will show RDY after you reconfigure and select Yes in the Confirm pop-up
window.
Note: In some operating systems, deleting an array and associated logical drives might change the drive letters assigned to the existing drives.

Creating a Disk Array
To create a disk array:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and
turning on the system. If the system already is on, press Ctrl+Alt+Del.
Note: To create an array using hard disks in an existing array, refer to Redefining Space in an Array.
2. Select Create/delete arrayfrom the Main Menu.
3. Select Create disk arrayfrom the Create/Delete Array menu.
The cursor will be active in the Bay/Array selection list.
Important: In the following step, when you press Enter to select a drive for an array, you cannot deselect it by
pressing Enter again, as you can with the hot-spare selection process. Carefully determine which drives you want to include in the array before beginning the selection process.
If you change your mind after selecting the drives for an array, you can delete the array (by selecting Delete disk array from the Create/Delete Array menu) and begin again.
4. Select each drive you want in the array by using the Up Arrow or Down Arrow to highlight the drive and then pressing Enter. As you select each drive, the status will change from RDY (Ready) to ONL (Online).
5. When you have selected all the drives you want to include in the array, press Esc. The cursor will become active in the menu.
6. If you have drives you did not use in this array and you want to create another array, you can do one of the following:
o Define the logical drive or drives for this array; then create another array and its logical drives. See Defining Logical Drives.
o Create another array now by repeating steps 2 through 5 in this procedure; then define logical drives for both arrays.
Note: You must define at least one logical drive for each created array before you can exit the configuration program.
o Continue with Defining Logical Drives.

Adding Drives to Create an Additional Array
To add storage capacity to your server without disturbing existing data:
1. Install the additional hard disk drive or drives. (See Installing Internal Drives.)
2. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
3. Create a new disk array and define logical drives (see Creating a Disk Array for detailed instructions).

Defining Logical Drives
After you have created an array, you must define a logical drive. (You cannot leave the RAID configuration program until you define the logical drives for any created arrays.)
To define a logical drive:
1. Select Define Logical drivefrom the Create/Delete Array menu. The cursor is active in the Array list.
2. Use the Up Arrow or Down Arrow to highlight the array you want to define; then press Enter. The Select RAID
Level pop-up window appears, and the cursor is active in the window.
Note: The system automatically assigns RAID level 0 to any logical drives defined in an array containing only one hard disk drive. When this is the case, the Select RAID Level pop-up window will not appear. If you have only two hard disk drives in the array, the Select RAID Level pop-up window appears, but RAID level 5 is not selectable because you need at least three hard disk drives in an array to assign RAID level 5 to one of the logical drives. You can define more than one logical drive for your array. The only restriction is that the maximum number of logical drives you can define is eight.
3. Use the Up Arrow or Down Arrow to highlight the RAID level you want to assign to these logical drives, then press Enter.
Note: Because the level you assign can influence the space needed for the drive, you must assign a RAID level before you enter the size of the logical drive. The Logical Drive list shows you the logical drive ID, the size of each logical drive, the RAID level you assigned to that logical drive, and the date that the logical drive was created.
The status of the logical drive also is shown. Good means that all is well with the drive. Critical means that you must replace the hard disk drive or do a rebuild operation. (You will have received a message telling you
what has happened to the drive.) Offline means that the logical drive is irrecoverable; the data on that drive is lost. The Logical Drive Size pop-up window shows the space in this array that is available for logical drives.
4. Type the size, in megabytes, that you want for the logical drive; then press Enter. A pop-up window appears
asking you to confirm your action.
Information about the new logical drive appears in the Logical Drive list.
Note: The size appearing in the Logical Drive list might be different from the size you typed because it appears
in binary equivalent. The size of a logical drive is determined by a number of factors, but basically the size must be divisible by the number of drives in the array.

Consider the following scenarios:
Scenario 1: There are three 1GB drives in the array. You assign RAID level 0 (which uses all the drives in the array with no parity storage), and type "1000MB". The "Size (MB)" will be 999, which is the number closest to and lower than 1000 that is divisible by 3. 
Scenario 2: There are three 1GB drives in the array, and you assign RAID level 5. Data is striped across all three drives in the array, but the space equivalent to that of one drive is used for redundant storage.
Therefore, if you type "1000MB", the "Size (MB)" remains 1000 because it is divisible by 2 (drives), which is the space available for data.
If you do not use the entire array for this logical drive, you can create another by assigning either the same or a different RAID level for an additional logical drive. You can have as many as eight logical drives among four disk arrays.
5. To return to the Create/Delete Array menu, press Esc. To define more logical drives, repeat steps 1 through 5 of this procedure.
6. To leave this screen, select Exit or press Esc. A pop-up window appears asking you to confirm your action.
7. To save your changes, select Yes. To maintain the disk-array configuration that was in place before you made changes, select No.
8. If you are using RAID level 1 or RAID level 5, you must select Initialize logical drivefor proper operation. This sets the drive to a predetermined state. Any data existing on the drive is overwritten with zeros, and corresponding parity is initialized to the correct value.
a. Select Initialize/synchronize arrayfrom the Main Menu; then select Initialize logical drive.
b. Select the logical drives you want to initialize from the Logical Drive list by pressing the Spacebar (the selected drives will appear highlighted). To start the initialization, press Enter. A pop-up window appears asking you to confirm your action.
Warning:If you select Yes in the Confirm pop-up window, information in the logical drive will be overwritten with zeros.
c. Select Yes to confirm that you want to initialize this logical drive.
The initialization process begins, and you can see its progress in the Pct. Int. (Percent Initialized) column of the Logical Drive list.
d. To stop the initialization at any time, press Esc. Then press Esc again to return to the menu, or press Enter to continue initializing the drive.
9. To back up the disk-array configuration to diskette, you will need a 3.5-inch formatted diskette. To back up the disk-array configuration:
a. Select Advanced functionsfrom the Main Menu.
b. Select Backup config. to diskette.
Follow the instructions on the screen. A pop-up window shows the default file name of CONFIG. You can change the file name by typing over the default. The Backup program will assign a file-name extension of .dmc.

Drive Maintenance
The following section provides information about status indicators for logical and hard disk drives, and the results of a hard disk drive failure. It also contains procedures for replacing defunct drives and for redefining the space in an array by replacing logical drives.
Subtopics:
o Obtaining Drive Status
o Results of a Hard Disk Drive Failure
o Logical and Hard Disk Drive Status Indications
o Replacing a Faulty Drive

Obtaining Drive Status
To see the ID, capacity, and other information about each of the hard disk drives attached to the RAID adapter:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
2. Select Drive information.
3. Use the Up Arrow or Down Arrow to highlight each of the drives shown in the Bay/Array selection list. As a drive is highlighted, the information for that drive is shown at the bottom of the screen.
4. Press Esc to return to the Main Menu.
Note: The status of the hard disk drive determines the status of the logical drives in the array in which the hard disk is grouped.
Subtopics:
o Bay/Array Selection List
o Blank Status

Bay/Array Selection List
The status of the drives in the Bay/Array selection list is defined as follows:
Status Meaning
CDR CD-ROM drive installed.
DDD Defunct. The drive is an online or hot-spare drive that does not respond to commands. (If a RDY drive is defunct or powered down, it shows an empty bay (a blank status), not a DDD status).
FMT Format. The drive is being reformatted.
HSP Hot spare. The drive will replace a similar drive that becomes defunct in real time. At that time, its status changes to ONL, and its array association is displayed.
OFL Offline. The drive is a good drive that has replaced a defunct drive in a RAID level 1 or level 5 array. It is associated with an array, but does not contain any valid data. The drive state remains OFL during the
rebuild phase.
ONL Online. The drive is part of an array. If this drive fails, logical drives defined in the array in which this
drive is grouped will have a status of offline (if the logical drive is assigned RAID level 0 with a good status) or Critical (if the logical drive is assigned RAID level 1 or level 5 with a good status).
RDY Ready. The drive is recognized by the adapter and is available for definition.
TAP Tape drive installed.
UFM Unformatted. The drive requires a low-level format before it can be used in an array.

Any of the following circumstances can cause the status area to be blank:
o No hard disk drive is installed in that bay.
o The bay contains a hard disk drive, but the drive is not inserted correctly.
o An array was deleted and a defunct drive is still in the bay.
o A new drive was installed and the configuration program has not been restarted. (The status will change to RDY when the RAID configuration program is restarted.)

Results of a Hard Disk Drive Failure
Depending on the circumstances, there can be several possible results from a drive failure.

Scenario 1:
o Only one hard disk drive fails.
o A hot-spare drive is defined that is the same or greater size than the failed drive.
o The logical drives in the array are assigned RAID level 1, level 5, or a combination of these two levels. Then the hot spare will take over immediately. Data for logical drives assigned RAID levels 1 and 5 is maintained; however, system performance will be reduced. Hot-spare drive capability does not apply to logical drives assigned RAID level 0.
Scenario 2:
o Only one hard disk drive fails.
o A hot-spare drive is not defined.
o The logical drives in the array are assigned RAID levels 1, 5, or a combination of these two levels. Then no data will be lost, but the system will operate at reduced performance until the defunct drive is replaced and rebuilt.
Scenario 3:
If more than one drive fails, all data is lost. Therefore, it is important that you replace and rebuild a defunct drive as soon as possible.

Logical and Hard Disk Drive Status Indications
The status of the hard disk drive determines the status of the logical drives in the array in which the hard disk is grouped.
o A single hard disk drive failure (indicated by a DDD status in the Bay/Array selection list) causes logical drives in that array that are assigned levels 1 and 5 to have a Critical status. Data remains in logical drives with a Critical status, but you must replace the one defunct hard disk drive promptly, because if two hard disk drives were to fail, all of the data in the array would be lost. After you install a new hard disk drive, the Replace process changes the drive status from DDDto OFL if there is
a Critical logical drive. After the Rebuild process, the hard disk drive status changes from OFL to ONL.
o A single or multiple hard disk drive failure causes logical drives in that array that are assigned level 0 to have an offline status. Data in logical drives with an offline status is lost. However, with a multipledisk drive failure, when the defunct drives are part of the same array, logical drives in that array will have an offline status. This means that data is lost in all the logical drives in that array, regardless of which RAID level is assigned.

Replacing a Faulty Drive
The hard disk drive indicator light will blink when the drive has failed and needs to be replaced (DDD state only). See Removing a Drive from Bank C, D, or E to locate the faulty hard disk drive.
To replace a faulty drive:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
If the drive failed while the system was powered down, a screen appears the next time the system is powered on showing you which drive is defunct.
2. If the drive is not damaged (for example, it is not inserted correctly):
a. Turn off the system.
b. Correct the problem.
c. Remove the diskette or ServerGuide CD from the drive.
d. Restart the system.
3. If the drive is defunct:
a. Press Y (Yes) to reconfigure the system.
b. Press Ctrl+Alt+Delwhen instructed to restart the system. The Main Menu appears.
c. Select Rebuild device. At this point, the drive status shows DDD.
Warning: Removing the wrong hard disk drive can cause loss of all data in the array.
d. Replace the defunct drive. Refer to Removing a Drive from Bank C, D, or E.
e. After you have replaced the drive, press Enter. The system will reconfigure to include the drive, and the driveís status will change to OFL.
f. Allow the system to complete the configuration (the screen displays a completion message); then select Rebuild drive.
g. Use the Up Arrow or Down Arrow to highlight the OFL (offline) drive you want to rebuild; then press Enter.
(The progress of the rebuilding process appears on the screen.)
h. When the rebuilding process completes, press Esc to return to the Main Menu. The new configuration will be saved automatically.
i. Backup the new configuration (see Backing Up Your Disk-Array Configuration).
j. Select Exit to end the RAID configuration program.
k. Remove the diskette and press Ctrl+Alt+Del to restart the system.

Redefining Space in an Array
You can redefine space in a disk array in a number of ways. For example, you can combine a number of small logical drives to create a larger one or you can redefine the existing logical drive into several smaller drives. Also, you can install additional hard disk drives to create a larger logical drive than was possible with the existing storage capacity.
One method to redefine space in an array is to change the RAID level assigned to a logical drive. For example, if you assigned RAID level 1 to a logical drive and then decided you needed the capacity offered with RAID level 5, you can use this procedure to replace the existing logical drive with a logical drive assigned the new RAID level. To redefine the space in a disk array, first you must delete the array. The last disk array defined must be the first deleted.
Warning:In all cases, when you delete an array, all the data and programs in the array are lost. If you have data and programs that you want to save, they must be backed up and then restored. It is suggested you use a high-speed backup device, such as a tape drive. To redefine the space in an array:
1. Back up all data and programs in the array.
2. If needed, install additional hard disk drives.
Refer to the Userís Referencefor information about selecting drive sizes.
3. Insert the IBM RAID controller diskette; then press Ctrl+Alt+Del to start the RAID configuration program.
4. Delete the existing array:
a. Select Create/delete arrayfrom the Main Menu. The Create/Delete Array menu will disappear.
b. Select Delete disk array. The cursor will be active in the Bay/Array list.
c. Review the Logical Drive List Date Created column; then press the Up Arrow or Down Arrow to highlight the most recently defined array.
Note: You must delete disk arrays in descending order; the last one created must be the first one deleted.
d. Press Del. The Confirm pop-up window appears.
Warning:All the data in the array will be lost during this procedure. Be sure to back up all data and programs that you want to save.
e. If you do not want to delete the array, select No. To delete the array select, Yes. Note: To use the hard disks from the existing array when creating a new array, you must confirm the deletion of the existing array. After you make your selection, the Confirm pop-up window will disappear, and the cursor will be active in the menu.
5. If you want a drive defined as a hot spare, refer to Defining a Hot-Spare Drive for step-by-step instructions.
6. Create a new disk array and define logical drives.
See Creating a Disk Array for instructions on creating a disk array and defining logical drives.
7. After you have established the new array and logical drive or drives, select Initialize/synchronize array from the Main Menu; then select Initialize logical driveto prepare the drives in the array to receive data. This sets the drive to a predetermined state. Any data existing in the drive is overwritten with zeros, and corresponding
parity is initialized to the proper value.
8. Insert a 3.5-inch formatted diskette in the primary drive, select Advanced functionsfrom the Main Menu; then select Backup config. to diskette.Follow the instructions on the screen.
9. Exit the RAID configuration program by pressing Esc or selecting Exit while on the Main Menu. A pop-up window will appear asking you to confirm your action.
10. Reinstall your operating system and device drivers, then restore your data and programs.

Advanced Functions
You can select several utilities from the Advanced Functions menu. They include:
o Backup configuration to diskette
o Restore configuration to diskette
o Change the write policy
o Change the RAID parameters
o Format a drive
Subtopics:
o Backing Up Your Disk-Array Configuration
o Restoring the Disk-Array Configuration
o Using the Advanced Functions

Backing Up Your Disk-Array Configuration
The RAID adapter maintains a record of the disk-array configuration information in its EEPROM (electronically erasable programmable read-only memory) module. The disk-array configuration is vital information. To protect this information, back up the information to diskette as soon as you have completed your tasks. You need a blank, formatted, 3.5-inch diskette.
To back up the disk-array configuration information to diskette:
1. Label the blank diskette "Disk Array Configuration Backup," and date it.
2. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
3. Select Advanced functionsfrom the Main Menu.
4. Select Backup config. to diskette.
5. Remove the RAID controller diskette from the drive and insert the blank diskette.
6. Follow the instructions on the screen.

Restoring the Disk-Array Configuration
To restore the disk-array configuration information in the RAID adapter EEPROM module, use the RAID controller diskette and an up-to-date Disk Array Configuration Backup diskette.
Note: Because dynamic changes in the configuration of your disk array occur due to hot-spare drive replacement or other drive maintenance activity, the configuration backup information on the diskette might be different from that in the adapter. It is important that you back up the disk-array configuration information frequently, to keep the backup information on the diskette current. To restore the RAID configuration information:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and
turning on the system. If the system already is on, press Ctrl+Alt+Del.
2. Select Advanced functionsfrom the Main Menu.
3. Select Restore config. from diskette.
4. Follow the instructions on the screen.

Using the Advanced Functions
This section gives the procedures for using the advanced functions, such as changing the write policy, changing the RAID parameters, and formatting a drive. Warnings appear throughout this section to alert you to potential loss of data and should be heeded before answering yes to the confirmations requested by the RAID configuration program.
Subtopics:
o Changing the Write Policy
o Formatting Drives
o Changing the RAID Parameters

Changing the Write Policy
When you configure a logical drive, the RAID adapter automatically sets the write policy to write-through(WT) mode, where the completion status is sent after the data is written to the hard disk drive. To improve
performance, you can change this write policy to write-back(WB) mode, where the completion status is sent after the data is copied to cache memory, but beforethe data is actually written to the storage device.
Although you gain performance with write-back mode, it creates a greater risk of losing data due to a power
failure. This is because the system gets a completion status message when the data reaches cache memory, but beforedata is actually written to the storage device.
To change the write policy:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
2. Select Advanced functionsfrom the Main Menu.
3. Select Change write policyfrom the Advanced Functions menu. The cursor will be active in the Logical Drive list.
4. Select the logical drive whose write policy you want to change. The Logical Drive list shows you the logical drive ID, the size in megabytes of each logical drive, the RAID level you assigned to that logical drive, and the date you created it. The status of the logical drive is also shown.
Good means that all is well with the drive. Critical means that you must replace the hard disk drive and rebuild the logical drive. (You will have received a message telling you what has happened to the drive.)
Offline means that the logical drive is irrecoverable; the data in that drive is lost.
5. Locate the Wrt pol (Write Policy) field in the Logical Drive list.
The write policy is shown as either WT (write-through, which is the default setting) or WB (write-back).
6. Use the Up Arrow or Down Arrow to select the logical drive whose write policy you want to change.
Warning:If you change the write policy to write-back, wait at least 10 seconds after your last operation before you turn off the server. It takes that long for the system to move the data from the cache memory to the storage device. Failure to follow this practice can result in lost data.
7. Press Enter to change the write policy. (Notice that WT changes to WB. You can press Enter to alternate between WT and WB.)
8. When you have made your choice, press Esc to return to the Advanced Functions menu.
9. Select Exit. The Confirm pop-up window appears asking you to confirm your action.
10. To return the setting to its original state, select No. To save your changes, select Yes.
11. Back up the disk-array configuration information to diskette. Refer to Backing Up Your Disk-Array Configuration for more information.

Formatting Drives
You can perform a low-level format on drives with RDY (ready), OFL (offline), or UNF (unformatted) status.
The Format drivechoice on the Advanced Functions menu provides a low-level format. If you install a new hard disk drive that requires a standard format, use the Format command provided by your operating system. The Format program works like the low-level format program in the advanced diagnostics portion of the system programs. It is provided in the IBM RAID configuration program so that you can perform a low-level format on a drive controlled by the RAID adapter.
To perform a low-level format:
1. Start the RAID configuration program by inserting the IBM RAID controller diskette into the primary drive and turning on the system. If the system already is on, press Ctrl+Alt+Del.
2. Select Advanced functionsfrom the Main Menu.
Warning:A low-level format erases all data and programs from the drive.
3. Select Format drive. The low-level format program starts.
4. Follow the instructions on the screen.
You can perform a low-level format on more than one drive at a time.

Changing the RAID Parameters
You can change the RAID parameters using the advanced functions by selecting Change RAID parameters.
The default settings are:
o Stripe unit size - 8K
The stripe unit size is the amount of data written on a given disk before writing on the next disk. To maximize the overall performance, this stripe unit should be chosen such that the stripe-unit size is close to the size of the system I/O request. The default is set to 8K data bytes.
Warning:Once the stripe unit is chosen and data is stored in the logical drives, the stripe unit cannot be changed without destroying data in the logical drives.
o Rebuild priority - Equal
Rebuild priority can be set to equal, high, or low. When set to equal, the rebuild I/O request and system I/O request get equal priority in the execution order. When set to high, the rebuild I/O request will get a higher priority than a system I/O request. In a heavily loaded system (with a high rate of system I/O requests), the high-priority rebuild can significantly reduce the disk rebuild time at the expense of degraded handling of I/O requests. When the rebuild priority is set to low, the rebuild I/O requests can execute only if there is no pending system I/O requests. In a moderate to heavily loaded system, low rebuild priority will increase the disk rebuild time significantly and provide better system performance.
Note: Rebuild priority can be changed without affecting data in the logical drives.
o Parity placement - RA
Warning:Once a parity placement scheme is chosen and data stored, it cannot be changed without destroying data.
Parity placement defines how parity is placed in the disk array with respect to data. The following illustration shows both the Left Symmetric (LS) and Right Asymmetric (RA) parity placement in a four-drive disk array. Here AAA, BBB, and CCC are the data stripe units, and PP0 is the corresponding parity. Similarly DDD, EEE, and FFF are the data stripe units, and PP1 is the corresponding parity.
Right Asymmetric (RA) Left Symmetric (LS)
Disk Disk Disk Disk   Disk Disk Disk Disk
 1    2    3    4      1    2    3    4
PP0  AAA  BBB  CCC    AAA  BBB  CCC  PP0
DDD  PP1  EEE  FFF    EEE  FFF  PP1  DDD
GGG  HHH  PP2  III    III  PP2  GGG  HHH
JJJ  KKK  LLL  PP3    PP3  JJJ  KKK  LLL
In some situations you may want to try LS parity placement to improve performance. The default parity placement is RA.
o Read ahead - On
Normally the IBM SCSI-2 Fast/Wide Streaming-RAID Adapter/A transfers data from disk to its local cache in steps of stripe-unit size. This provides excellent overall performance when workloads tend to be sequential. However, if the workload is random and system I/O requests are smaller than stripe-unit size, reading ahead to the end of the stripe unit will result in a wasted SCSI bus bandwidth and wasted disk utilization. When read-ahead is set to Off, the size of data transfer from the disk to local cache is equal to the system I/O request size, and no read-ahead to the end of the stripe unit is performed.

Notes:
1. The Read-ahead setting can be changed without destroying data in a logical drive.
2. When the configuration is saved on a diskette, the RAID parameters are saved also.

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