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
94 HP StorageWorks HSG60 and HSG80 Array Controller and Array Controller Software
Command Line Interface Reference Guide
The following describes how to specify the PREFERRED_PATH switch:
■ If no preferred path is assigned, the unit is targeted through the controller
that detects the unit first after the controllers start.
■ Select PREFERRED_PATH=THIS_CONTROLLER to instruct “this
controller” to bring this unit online.
■ Select PREFERRED_PATH=OTHER_CONTROLLER to instruct the
“other controller” to bring this unit online.
Note: All partitions on a container must be addressed through the same controller. If
you set the preferred path for one partition, all partitions on that container inherit the
same preferred path setting.
READ_CACHE (default)
NOREAD_CACHE
Sets the controller read-cache policy function. If READ_CACHE is selected
and the controller receives a read request from the host, the following events
occur: the controller reads the data from the disk drives, delivers it to the host,
and stores the data in its cache module. Subsequent reads for the same data
takes the data from cache rather than access the data from disks.
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 since only a small amount of data is cached. 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 tries to keep ahead of the host by reading
the next sequential blocks of data (those the host has not yet requested) and
putting the data in cache. This process is sometimes referred to as prefetching.
The controller can detect multiple sequential I/O requests across multiple
units.