HP StorageWorks HSG60 and HSG80 Array Controller and Array Controller Software Command Line Interface Reference Guide (EK-G80CL-RA. C01, March 2005)

CLI Command Descriptions
241HP StorageWorks HSG60 and HSG80 Array Controller and Array Controller Software
Command Line Interface Reference Guide
READ_CACHE (default)
NOREAD_CACHE
Controls how and where the controller retrieves previous read request data
and submits that data to the host.
■ Specify READ_CACHE to direct the controller (after it receives a read
request from the host), to read the data from the disk drives, deliver it to
the host, and store the data in its cache module. Subsequent reads for the
same data takes the data from cache rather than accessing the data from
the disks.
■ Specify NOREAD_CACHE to prevent the controller (after it receives a
read request from the host), from reading the data from the disk drives,
delivering it to the host, and storing the data in its cache module.
Read caching improves performance in almost all situations. Therefore, HP
recommends that you leave its default setting, READ_CACHE, enabled.
However, under certain conditions, such as when performing a backup, read
caching may not be necessary because the data is probably not re-read. In
such instances, it can be beneficial to disable the read cache function and
remove the processing overhead associated with caching data.
READAHEAD_CACHE (default)
NOREADAHEAD_CACHE
Enables the controller to keep track of read I/Os. If the controller detects
sequential read I/Os from the host, it then tries to keep ahead of the host by
reading the next sequential blocks of data (those the host has not yet
requested) and put the data in cache. This process is sometimes referred to as
prefetch. The controller can detect multiple sequential I/O requests across
multiple units.
Read-ahead caching improves host application performance because the data
is read from the controller cache instead of disk. Read-ahead caching is the
default for units.
If you have a unit that is not expected to get sequential I/O requests, select
NOREADAHEAD_CACHE for the unit.