Phoenix RPC12 Series, Cli Reference Manual

Page: 102 / 245

Chapter 3 Command Descriptions 103
set cache-parameters
Description
Sets the RAID controller cache policy and cache optimization mode for a specified
volume.
Note – Only change the read-ahead 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.
Q
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.
Q
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 101.
Cache Optimization Mode
Before creating or modifying a volume, determine the appropriate cache
optimization mode. The controller supports
super-sequential
optimization
mode for sequential I/O and
standard
optimization mode for random I/O.
The cache optimization mode setting for each volume optimizes the cache block
size used by the controller:
Q
For sequential optimization, the cache block size is 128 Kbyte.
Q
For random optimization, the cache block size is 32 Kbyte.