Avago Technologies 3ware SAS 9750-4i - Manual (Page 101)

Unit Object Commands
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Read Cache Basic Mode is used to store read cache data locally on the
controller that has recently been written to media and is likely to be frequently
accessed. This improves read access times for applications such as a database
that can take advantage of storage caching. The read cache may be disabled
without reducing performance for applications that are write intensive, or that
rarely read back data recently written..
Read Cache Intelligent Mode enables the Intelligent Read Prefectch (IRP)
feature.
The Intelligent Read Prefetch feature includes a typical read-ahead caching
method which is used to proactively retrieve data from media and store it
locally on the controller with the anticipation that it may be requested by the
host. For example, the host may read blocks 1, 2, and 3. With the read-ahead
caching included in IRP, the controller will also retrieve and hold in its cache
blocks 4, 5, and 6 in anticipation of getting those command requests from the
host. By loading a larger set of data into the cache, chances are improved that
another request can be filled by data that is already in the cache. This can be
helpful with applications that are sequential in nature, such as video on
demand, video surveillance playback, and restoring from a disk-to-disk
backup. Performance benefits of read-ahead are especially pronounced when
the host queue depth is low. In addition, read-ahead caching also improves
sequential read performance when the unit is degraded.
The Intelligent Read Prefetch (IRP) feature also includes an adaptive stream
management layer to improve performance at higher queue depths in multiple
read only or mixed read/write stream environments. The performance
improvements should be seen for most RAID types regardless of the unit’s
operating unit state (normal, degraded, and so forth).
Example:
//localhost> /c0/u0 set rdcache=basic
Setting Read Cache Policy on /c0/u0 to [basic] ... Done.
/c x /u x set identify=on|off
This feature only applies to 9750 model controllers and 9000 series SX/SE/
SA model controllers.
This feature requires a supported enclosure. For additional information about
enclosure-related commands, see “Enclosure Object and Element
Commands” on page 122.
This command allows you to identify a unit within an enclosure by blinking
the LEDs associated with the drive slots of the specified unit.
Example:
//localhost> /c0/u0 set identify=on
Sending Identify request for unit /c0/u0 to [on] ... Done.