HP XP Racks - Manual (Page 94)

Figure 49 Flow of failovers and failbacks
The Continuous Access Synchronous Consistency preservation function
Continuous Access Synchronous Z provides storage system functionality that preserves the consistency
of the volume update sequence for each copy pair, even if a failure occurs on a volume or line.
This function is called the Continuous Access Synchronous consistency preservation function.
The Continuous Access Synchronous consistency preservation function preserves the consistency
of all copy pairs within a Continuous Access Synchronous Z copy group that has a consistency
group ID specified. By preserving the consistency among multiple copy pairs within a copy group,
the files within copy groups on the S-VOL side can maintain the status immediately preceding a
failure (or during a planned outage).
NOTE: For a Continuous Access Synchronous Z copy group without a consistency group ID
specified, the storage system preserves the consistency for each copy pair only.
To set up the Continuous Access Synchronous Consistency Preservation Function, see “Configuration
definition for using the Continuous Access Synchronous Consistency Preservation function” (page 139) .
To preserve Continuous Access Synchronous Z consistency, execute a script containing the
YKCONMSG
, YKFREEZE, YKSUSPND and YKRUN commands as follows:
1. When the YKCONMSG command is executed, Business Continuity Manager monitors operating
system messages for detecting a hardware failure.
2. When a failure is detected, the following three commands are executed in the order shown,
and copy processing for all copy pairs within the copy group is executed.
•
YKFREEZE : Freezes the copy group in order to suspend update (I/O) operations from
the host to all volumes within the copy group. This status is called the SCP status.
•
YKSUSPND : Suspends copy processing among all copy pairs within the copy group.
•
YKRUN : Releases volume updates that were held and allows I/O operations to resume.
If you need to acquire the copy group status, execute the YKRUN command, and then execute
either the YKQUERY or the YKEWAIT command.
94 Understanding Business Continuity Manager functions