Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 90)

Chapter 2. CLI Syntax Reference
82 3ware SATA+SAS RAID Controller Card CLI Guide, Version 10.2
/cx/ux set rdcache=basic|intelligent|off
The /cx/ux set rdcache command allows you to set the read cache to either
Basic, Intelligent, or Off on a specified unit. Setting this to Intelligent
enables both Intelligent Mode features and Basic Mode features. Setting it to
Off disables both.
Read Cache Basic Mode is used to store data that has been written recently
to media and is likely to be frequently accessed, to the read cache on the
controller. This improves read access times for applications such as a database
that can take advantage of storage caching. The read cache can 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 that is used to proactively retrieve data from media and store it locally
on the controller so that it can be requested by the host. For example, the host
might read blocks 1, 2, and 3. With the read-ahead caching included in IRP,
the controller also retrieves and holds blocks 4, 5, and 6 in its cache in case
the host requests the data. 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 queue depth of the host 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 with larger queue depths in
multiple read-only or mixed read/write stream environments. The
performance improvements can be expected for most RAID types regardless
of the unit’s operating state (normal, degraded, and so forth).
Example:
//localhost> /c0/u0 set rdcache=basic
Setting Read Cache Policy on /c0/u0 to [basic] ... Done.