Alternate Command Device Function - Hitachi VSP F1500 User And Reference Manual

# horcctl -DI
Current control device = /dev/rdsk/c0t0d0 AI = 14 TI = 0 CI = 1
Example with command device security:
# horcctl -DI
Current control device = /dev/rdsk/c0t0d0* AI = 14 TI = 0 CI = 1
AI: NUM of actual instances in use
TI: NUM of temporary instances in RAID
CI: NUM of instances using current (own) instance

Alternate command device function

The CCI software issues commands to the command device via the UNIX/PC
raw I/O interface. If the command device fails in any way, all CCI commands
are terminated abnormally, and you cannot use any commands. Because the
use of alternate I/O path is platform dependent, restrictions are placed upon
it. For example, on HP-UX systems, only devices subject to the LVM can use
the alternate path PV-LINK. To avoid command device failure, CCI supports
an alternate command device function.
Note: When you set a redundant path to the command device by using
alternate path software, make sure that path switching occurs only in case of
a failure. For example, you cannot use round robin.
• Definition of alternate command devices. To use an alternate
command device, you must define two or more command devices for the
HORCM_CMD item in the configuration definition file. When two or more
devices are defined, they are recognized as alternate command devices.
Create all alternate command devices within the same resource group of
the same storage system.
• Timing of alternate command devices. When the HORCM receives an
error notification in reply from the operating system via the raw I/O
interface, the alternate command device is used. You can also change to
the alternate command device forcibly by using the horcct1 -C switch
command. However, if you specified HORCM_CMD for the volume
belonging to a virtual storage machine, you cannot use the horcct1 -C
switch command, and therefore you cannot switch to the alternate
command device forcibly.
• Operation of alternating command. If the command device is blocked
due to online maintenance, the switch command should be issued in
advance. If the switch command is issued again after completion of the
online maintenance, the previous command device is activated.
• Multiple command devices on HORCM startup. If at least one
command device is available during one or more command devices
described to the configuration definition file, then HORCM can start with a
warning message to the startup log by using the available command
device. Confirm that all command devices can be changed by using the
horcctl -C command option, or HORCM has been started without the
warning message to the HORCM startup log.
CCI software environment
Command Control Interface User and Reference Guide
2-5