HP XP7 Storage - Manual (Page 19)

to the LVM can use the alternate path PV-LINK. To avoid command device failure, RAID Manager
supports an alternate command device function.
•
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.
•
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. It is possible to force a switch to use the alternate the command device by issuing the
horcctl -C switch command provided by RAID Manager.
•
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.
Figure 4 Alternate command device function
Define the remote command device
The command device of external storage system that is mapped as a command device of the local
storage system is called as remote command device. By issuing a command to the remote command
device, the operation at the external storage system is realized.
The remote command device is defined by the Remote Web Console. For more information, see
the HP XP7 External Storage for Open and Mainframe Systems User Guide.
RAID Manager and the SCSI command interface
When RAID Manager commands are converted into a special SCSI command format, a SCSI
through driver that can send specially formatted SCSI commands to the RAID storage system is
needed. As a result, OS support for RAID Manager depends on the OS capabilities. It is necessary
to use a read/write command that can easily be issued by many UNIX/PC server platforms. For
example, ioctl() can be used for the following platforms: HP-UX, Linux, Solaris, Windows, IRIX64,
OpenVMS and zLinux.
SCSI command format used. Use a RD/WR command that can be used with special LDEVs, since
they should be discriminated from the normal RD/WR command.
RAID Manager components on the RAID storage system 19