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66 Chapter 2 Overview of CCI Operations
2.8.7.1 Command Competition
The CCI commands are asynchronous commands issued via the SCSI interface. Accordingly, 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 WR commands should not be issued
to a single LDEV. The command initiators should not issue two or more WR commands to a
single LDEV unless the storage system can receive commands with independent initiator
number * LDEV number simultaneously.
Hitachi RAID
(Command device)
RD/WR command
Command
process
HORCM
(CCI)
Command
process
Command
process
Figure 2.34 HORCM and Command Issue Process
2.8.7.2 Flow of Commands
Figure 2.35 shows the flow of RD/WR command control in a specified LBA#.
Write()
Command area
Input parameter
Edited data
Input data
Read()
Write/read
processing code
Scanning edit data by reading
LDEV (Target#, LUN#)
Host side Hitachi RAID side
Figure 2.35 Flow of Command Issue