Changing the RAID Parameters

Changing the RAID Parameters

You can use the ServeRAID Configuration program to set the stripe-unit size, to set the rebuild priority, to turn Unattended Mode On or Off, or to turn Read Ahead On or Off.

To change the RAID parameters:

Start the ServeRAID Configuration program (see 'Starting the ServeRAID Configuration Program').
Select Advanced Functions from the Main Menu, then, press Enter.
Select Change RAID parameters from the next menu, then, press Enter.

A screen similar to the following appears.

Descriptions of the RAID parameters that you can change are as follows:

Stripe Unit Size: The default setting is 8K data bytes.

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, choose a size that is close to the size of the system I/O request.

Note: The size of the system I/O request depends on the operating system. If you are not sure of the size, use the default setting.

After you set a stripe-unit size and store data in the logical drives, you cannot change the size without destroying data in the logical drives.

You can set the stripe-unit size to 8 K, 16 K, 32 K, or 64 K.

When the stripe-unit size is 8 K or 16 K, the maximum number of physical drives in an array is 16.
When the stripe-unit size is 32 K or 64 K, the maximum number of physical drives in an array is eight.

Rebuild Priority: The default setting is High. The rebuild priority can be set to High, Medium, or Low.

When the rebuild priority is set to High, the rebuild I/O request gets highest priority in the execution order.
When the rebuild request is set from High to Medium in a heavily loaded system, it can increase the disk rebuild time, but provide better system performance.
When the rebuild request is set from High or Medium to Low in a moderate to heavily loaded system, it can increase the disk rebuild time, but provide better system performance.

Unattended Mode: The default setting is Off. You can enable the ServeRAID controller to accept changes in the configuration without user input.

When unattended mode is set to Off, the program waits for user input when an event is detected.

When unattended mode is set to On, the ServeRAID controller pauses briefly to permit a user to override the default action, then, the controller makes the necessary changes. Unattended mode also clears any blocked drives. This mode is useful when the server operates remotely.

When unattended mode is set to On, the ServeRAID controller 'chooses' an action that is equivalent to pressing one of the function keys.

Note: When F5 is selected, non-responding ONL and RBL drives become DDD, RDY and SBY drives become EMP, and HSP drives become DHS.

F5: The server continues the startup operation after identifying a defunct drive. For example, an HSP drive failed to respond during POST. Startup continues, but the ServeRAID controller changes the state of the HSP drive to DHS.

F6: When a drive is removed from the server (for example, for maintenance or security), but is returned to a different bay, the ServeRAID controller adjusts the configuration to the drive's new location.

F7: A ServeRAID controller, with stored configuration information that does not match that of the configured drives present, imports the configuration information from the drives.

Read Ahead: The default setting is On.

Normally, the ServeRAID controller transfers data from disk to its local cache in increments equal to the stripe-unit size. This provides excellent overall performance when workloads are steady and sequential. However, if the workload is random or the system I/O requests are smaller than the stripe-unit size, reading ahead to the end of the stripe might degrade performance.

When read ahead is set to Off, the ServeRAID controller transfers data from disk to its local cache in increments equal to the system I/O request size, without reading ahead to the end of the stripe.

You can change the read-ahead setting without destroying data in a logical drive.

Use the Up Arrow ( ), Down Arrow ( ), Right Arrow (>), or Left Arrow (<) key to highlight the parameter that you want to change, then, press Enter.

Press Esc to return to the Advanced Functions menu.
Back up the disk-array configuration information to diskette. See 'Backing Up the Disk-Array Configuration' for instructions. (The backup procedure also saves the RAID parameters to diskette.)

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