Setting The Modification Priority - IBM System Storage DS3000 Programming Manual

To enable write caching with mirroring, set this parameter to TRUE. To disable write caching with
mirroring, set this parameter to FALSE. This example shows how to set this parameter:
c:\...\...\client>smcli 123.45.67.89 -c "set logicalDrive
[\"Accounting\"] mirrorCacheEnabled=TRUE;"
The readCacheEnabled parameter turns on or turns off the ability of the host to read data from the cache.
Read caching enables read operations from the host to be stored in controller cache memory. If a host
requests data that is not in the cache, the controller reads the needed data blocks from the disk drives
and places them in the cache. Until the cache is flushed, all of the other requests for this data are fulfilled
with cache data rather than from a read, which increases throughput. To enable read caching, set this
parameter to TRUE. To disable read caching, set this parameter to FALSE. This example shows how to set
this parameter:
c:\...\...\client>smcli 123.45.67.89 -c "set logicalDrive
[\"Balance_04\"] readCacheEnabled=TRUE;"
The writeCacheEnabled parameter turns on or turns off the ability of the host to write data to the cache.
Write caching enables write operations from the host to be stored in cache memory. The logical drive data
in the cache is automatically written to the disk drives every 10 seconds. To enable write caching, set this
parameter to TRUE. To disable write caching, set this parameter to FALSE. This example shows how to set
this parameter:
c:\...\...\client>smcli 123.45.67.89 -c "set allLogicalDrives
writeCacheEnabled=TRUE;"
The cacheReadPrefetch parameter turns on or turns off the ability of the controller to read additional
data blocks into cache. When you turn on cache read prefetch, the controller copies additional data blocks
into cache while it is reading requested data blocks from a disk drive into cache. This action increases the
chance that a future request for data can be fulfilled from the cache, which improves the speed with
which data is accessed. The number of additional data blocks that the controller reads into cache is
determined by the storage subsystem configuration settings that you use. Cache read prefetch is
important for applications that use sequential I/O, such as multimedia applications.
Valid values for the cacheReadPrefetch parameter are TRUE or FALSE. If you want to turn on cache read
prefetch, set the cacheReadPrefetch parameter to TRUE. If you want to turn off cache read prefetch, set the
cacheReadPrefetch parameter to FALSE. This example shows how to set this parameter:
c:\...\...\client>smcli 123.45.67.89 -c "set logicalDrive
[\"Engineering_1\" \"Engineering_2\"] cacheReadPrefetch=TRUE;"

Setting the Modification Priority

Modification priority defines how much processing time is allocated for logical drive modification
operations. Time allocated for logical drive modification operations affects system performance. Increases
in logical drive modification priority can reduce read/write performance. The modification priority
affects these operations:
v Copyback
v Reconstruction
v Initialization
v Changing the segment size
v Defragmentation of an subsystem
v Adding free capacity to an subsystem
v Changing the RAID level of an subsystem
The lowest priority rate favors system performance, but the modification operation takes longer. The
highest priority rate favors the modification operation, but the system performance might be degraded.
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Chapter 4. Configuring a Storage Subsystem