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Hitachi Command Control Interface (CCI) User and Reference Guide 63
2.8.5 Command Device
The Hitachi TrueCopy/ShadowImage commands are issued by the HORC Manager (HORCM) to
the RAID storage system command device. The command device is a user-selected,
dedicated logical volume on the storage system which functions as the interface to the CCI
software on the UNIX/PC host. The command device is dedicated to CCI communications and
cannot be used by any other applications. The command device accepts TrueCopy and
ShadowImage read and write commands that are executed by the storage system. The
command device also returns read requests to the UNIX/PC host. The volume designated as
the command device is used only by the storage system and is blocked from the user. The
command device uses 16 MB, and the remaining volume space is reserved for CCI and its
utilities. The command device can be any OPEN-x device (e.g., OPEN-3, OPEN-8) that is
accessible by the host. A LUSE volume cannot be used as a command device. A Virtual
LVI/LUN volume as small as 36 MB (e.g., OPEN-3-CVS) can be used as a command device.
WARNING: Make sure the volume to be selected as the command device does not contain
any user data. The command device will be inaccessible to the UNIX/PC server host.
The CCI software on the host issues read and write commands to the command device. When
CCI receives an error notification in reply to a read or write request to the RAID storage
system, the CCI software will switch to an alternate command device, if one is defined. If a
command device is blocked (e.g., online maintenance), you can switch to an alternate
command device manually. If no alternate command device is defined or available, all
Hitachi TrueCopy and ShadowImage commands will terminate abnormally, and the host will
not be able to issue commands to the storage system. The user must set one or more
alternate command devices (see section 2.8.6) to avoid data loss and storage system
downtime.
Each co
mmand device must be set using the LUN Manager remote console software. If the
remote LUN Manager feature is not installed, please ask your Hitachi Data Systems
representative about LUN Manager configuration services. Each command device must also
be defined in the HORCM_CMD section of the configuration file for the CCI instance on the
attached host. If an alternate command device is not defined in the configuration file, the
CCI software may not be able to use the device. See section 2.9 for instructions on setting
and defin
ing command devices.
The CCI Protection Facility (see section 4.16) uses an enhanced command de
vice which has
an attribute to indicate protection ON or OFF.
Notes:
For Solaris operations, the command device must be labeled.
To enable dual pathing of the command device under Solaris systems, make sure to
include all paths to the command device on a single line in the HORCM_CMD section of
the configuration file. Figure 2.31 shows an example with two controller paths (c1 and
c2) to the command device. Putting the path inf
ormation on separate lines may cause
parsing issues, and failover may not occur unless the HORCM startup script is restarted
on the Solaris system.