HP storageworks HSG80 Reference Manual page 54

CLI Command Descriptions
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 putting 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 is read
from the controller cache instead of disk. Read-ahead caching is the default for
units.
If you are adding a unit that is not expected to get sequential I/O requests, select
NOREADAHEAD_CACHE for the unit.
RUN (default)
NORUN
Controls the unit's 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 all the disks
used in the unit. The drives making up the unit spin down after the data has
been completely flushed.
NOTE: Do not specify the RUN /NORUN switches for partitions.
WRITE_LOG
NOWRITE_LOG (default)
Marks the defined unit as an OpenVMS Host Based Volume Shadowing shadow
set member.
IMPORTANT: This switch is only supported with ACS version 8.7R or version 8.7W code.
NOTE: The specified unit is only marked and not enabled.
To enable a unit as an OpenVMS Host Based Volume Shadowing shadow set
member, a single controller or both controllers of a dual redundant pair must be
restarted. During the restart, the additional memory structures required for GWHL
are allocated and initialized. Once enabled, the unit can only be disabled as an
OpenVMS Host Based Volume Shadowing shadow set member by use of the
NOWRITE_LOG command. When the log unit is disabled, it is not necessary to
restart the controllers—this needs to be done only when a log unit is enabled. Log
units can be JBODs,
be a member of a Snapshot or Remote Copy set.
When a SHOW unit-number command is entered for a given unit, one of the
following is displayed in the subsequent unit status display:
2–38
tripesets, RAIDsets, or mirrorsets. However, this unit cannot
s
HSG80 Array Controller V8.7 Command Line Interface Reference Guide