HP XP P9500 Storage - Manual (Page 18)

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 XP P9000 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.
Recognition of the control command area (LBA#). The host issues control commands through the
raw I/O special file of a special LDEV. Since the specific LU (command device) receiving these
commands is viewed as a normal disk by the SCSI interface, the OS can access its local control
area. The RAID storage system must distinguish such accesses from the control command accesses.
Normally, several megabytes of the OS control area are used starting at the initial LBA#. To avoid
using this area, a specific LBA# area is decided and control commands are issued within this area.
The command LBA# recognized by the storage system is shown below, provided the maximum
OS control area is 16 MB.
18 RAID Manager software environment