HP Array Controller HSG V8.7 Software - Manual (Page 412)

B–140 HSG80 User’s Guide
Select PREFERRED_PATH=THIS_CONTROLLER to instruct “this
controller” to bring the unit online.
Select PREFERRED_PATH=OTHER_CONTROLLER to instruct the
“other controller” to bring the unit online.
See Chapter 2 for information regarding multiple bus failover.
READ_CACHE (Default)
NOREAD_CACHE
Switches enable or disable the read-cache function for the unit.
Read caching improves performance in almost all situations, so it is
generally recommended to leave it enabled. However, under certain
types of conditions, such as when performing a backup, read-caching
may not be necessary since only a small amount of data is cached. In
such instances, it may be beneficial to disable read cache and remove
the processing overhead associated with caching.
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 will then try 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 since the
data will be read from the controller cache instead of disk. Read ahead
caching is the default for units.
If you do not expect this unit to get sequential I/O requests, select
NOREADAHEAD_CACHE for the unit.
RUN (Default)
NORUN
Controls the disk drive’s operation and availability to the host. Specify
RUN to make a unit available to the host. Specify NORUN to make a
unit unavailable to the host and to cause any data in cache to be flushed
to one or more drives. NORUN spins down the devices making up a