Hp StorageWorks 2000 Family Modular Smart Array CLI reference guide (481600-002, May 2008)

110 HP StorageWorks 2000 Family Modular Smart Array CLI reference guide • May 2008
set cache-parameters
Description
Sets cache options for a specific volume, or the cache redundancy mode for a dual-
controller storage system.
Note – Only change cache settings if you fully understand how your operating
system, application, and HBA move data so that you can adjust the settings
accordingly. Be prepared to monitor system performance using the virtual disk
statistics and adjust read-ahead size until you find the optimal size for your
application.
Cache Policy
The cache policy setting for each volume determines when cached data is written to
the disk drives. The ability to hold data in cache while it is being written to disk can
increase storage device speed during sequential reads.
■ Write-back caching does not wait for data to be completely written to disk before
signaling the host that the write is complete. This is the preferred setting for a
fault-tolerant environment because it improves the performance of write
operations and throughput. Write-back caching is enabled by default.
■ Write-through caching significantly impacts performance by waiting for data to
be completely written to disk before signaling the host that the write is complete.
Use this setting only when operating in an environment with low or no fault
tolerance.
You can configure the write policy to automatically change from write-back cache
to write-through cache when certain environmental events occur, such as a fan
failure. For details, see “set auto-write-through-trigger” on page 107.