User`s guide

StorageWorks RAID Array 200 Controller Installation and Standalone Configuration Utility
6–42 EK–SWRA2–IG. C01
6.6.2.2 Choosing a Caching Policy
The caching policy determines what procedure the RAID controller uses to write
data to the logical drives. You can choose one of the following caching policies:
• Write-Back caching: A caching policy in which the controller
acknowledges that a write operation has completed successfully before
data is written to the disks. If you choose this caching policy, you may
increase the I/O performance of your RAID subsystem.
We recommend that you select this caching policy only if your cache has
battery backup and you have enabled the battery backup. Without a
battery backup, if there is a power failure, you lose data in cache that is
not yet written to the disks.
• Write-Through caching: A caching policy in which the data is written to
disk before the controller acknowledges that a write operation is
completed successfully. If you choose this caching policy and there is a
power failure, you do not need a battery backup to minimize the chance of
data loss. This is the StorageWorks RAID Array 200 subsystem default
caching policy.
NOTE
We strongly recommend a Write-Through for the
EISA controller or any controller without battery
backup cache.
To change the caching policy, follow these steps:
1. Select the Toggle Write Policy option on the Logical Drive Definition menu.
The cursor moves to the Write Mode column of the logical RAID drives list
and highlights the write mode of the first logical RAID drive.
2. Press the Enter key to toggle the caching policy to Write-Back.
3. Use the arrow keys to move to another logical RAID drive and repeat Step 2
for each logical RAID.
4. When you finish selecting cache policy for your logical RAID drives, press
the Esc key once. You return to the Logical Drive Definition menu.
5. Press the Esc key again to return to the New Configuration menu.
If you plan to use one or more of your drives as a spare drive, go on to Section
6.6.3 to define a hot spare drive. Otherwise, go to Section 6.6.4 to save the
configuration of your array.