HP Modular Smart Array 500 Starter Kit Uživatelská příručka stáhnout pdf (Strana 80)

Cache write policy

The cache policy setting for each volume determines when cached data is written to the disks. 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.

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:

• For sequential optimization, the cache block size is 128 Kbyte.

• For random optimization, the cache block size is 32 Kbyte.

An appropriate cache block size improves performance when a particular application uses either large or

small stripe sizes:

• Video playback, multimedia post-production audio and video editing, and similar applications read

and write large files in sequential order.

• Transaction-based and database update applications read and write small files in random order.

Since the cache block size works in conjunction with the default stripe size set by the cache optimization

mode for each volume you create, these default stripe sizes are consistent with the cache block size setting.

You can, however, specify a different stripe size for any volume at the time you create it. For more

information, see create volume.

independent enable|disable

Sets the cache redundancy mode for a dual-controller storage system. enable sets the system's

operation mode to Independent Cache Performance Mode. When this mode is enabled, controller

failover is disabled and write-back cache is not mirrored to the partner controller. This results in

improved write performance but at a risk of loss of unwritten data if a controller failure occurs while

there is data in the controller's cache memory. Independent mode is disabled by default.

Example Set the cache policy and cache optimization mode for volume V1:

# set cache-parameters V1 optimization super-sequential read-ahead-size maximum

Success: Command completed successfully. - Cache parameters were changed

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HP Modular Smart Array 500 Starter Kit Uživatelská příručka Strana 80