HP XP7 Storage - Manual (Page 20)

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.
Figure 5 Relationship of the special file to the special LDEV
Acceptance of commands. A command is issued in the LBA area of the special LDEV explained
above. The RD/WR command meeting this requirement should be received especially as a RAID
Manager command. A command is issued in the form of WR or WR-RD. When a command is
issued in the form of RD, it is regarded as an inquiry (equivalent to a SCSI inquiry), and a RAID
Manager recognition character string is returned.
Command competition
The RAID Manager commands are asynchronous commands issued via the SCSI interface. As a
result, if several processes issue these commands to a single LDEV, the storage system cannot take
the proper action. To avoid such a problem, two or more write commands should not be issued
to a single LDEV. The command initiators should not issue two or more write commands to a single
LDEV unless the storage system can receive commands with independent initiator number * LDEV
number simultaneously.
Figure 6 HORCM and command issue process
Command flow
This figure shows the flow of read/write command control for a specified LBA#.
20 RAID Manager software environment