Avago Technologies 3ware SAS 9750-16i4e - Manual (Page 116)

Chapter 7. Configuring Units
104 3ware SATA+SAS RAID Controller Card Software User Guide, Version 10.2
Working with Read Cache Settings
The Read Cache unit policy lets you enable either Basic Read Caching or
Intelligent Read Caching. You can also disable the Read Cache unit policy, if
preferred.
By default, Read Cache is set to Intelligent . You can change it to Basic or to
Disabled , as appropriate.
About the Read Cache Basic and Intelligent Modes
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.
Intelligent Mode enables the Intelligent Read Prefetch (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, this read-ahead caching also
improves sequential read performance when the unit is degraded.
The Intelligent Read Prefetch (IRP) feature also includes an intelligent and
adaptive stream management layer to improve performance at higher queue
depth 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 operational state (normal, degraded, and so forth).
Note that if Intelligent Mode is enabled, the features in Basic mode are also
enabled.