HP XP7 Storage User Manual
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S-VOLs in chronological order (older data are restored earlier). This ensures that the update sequence
is maintained. For details on the time stamping function, see
“Host I/O time stamp ” (page 26)
.
The following does not apply to RAID Manager consistency groups with both Cnt Ac-J and Cnt
Ac-J Z journals:
•
The term “arbitration processing" refers to the maintenance of the data update sequence
through the execution of the journal restore function based on time stamps. When there is
more than one secondary storage system, one of them is used to perform tasks, including
arbitration processing, on the other secondary systems. The secondary storage system that
performs arbitration processing is called the “supervisor DKC”. Systems that are controlled
by the supervisor DKC and are targets of arbitration processing are called “subordinate DKCs”.
•
The supervisor DKC compares time stamps of data received by all the secondary systems
(including the primary system) and then performs arbitration processing. The supervisor DKC
must be connected with the subordinate DKCs.
Note the following when planning for multiple systems:
•
Remote Web Console is required at the primary and secondary sites.
•
BCM is required on the host at the primary and secondary sites.
If including Cnt Ac-J and Cnt Ac-J Z journals together, RAID Manager is required on the
mainframe host.
•
A remote command device for BCM must be created in the supervisor DKC. For details on
secondary systems connections and remote command devices, see
between multiple secondary systems ” (page 34)
•
Journal data is updated in the secondary system based on the time stamp issued from the
mainframe host (or RAID Manager if including Cnt Ac-J Z and Cnt Ac-J journals) and the
sequence number issued by the host with write requests to the primary system. Time and
sequence information remain with the data as it moves to the master and restore journals and
then to the secondary volume.
•
With RAID Manager consistency groups, when a pair is split from the S-VOL side (P-VOL status
= PAIR), each storage system copies the latest data from the P-VOLs to the S-VOLs. P-VOL time
stamps might differ by storage system, depending on when they were updated.
•
Disaster recovery can be performed with multiple storage systems, including those with Cnt
Ac-J and Cnt Ac-J Z journals, using RAID Manager. See
“Switching host operations to the
for information
•
Time stamps issued by RAID Manager and the mainframe host are different. The time stamps
issued by the mainframe host become invalid when the Cnt Ac-J Z journal is included in a
RAID Manager consistency group.
•
Restoring data to the secondary system is performed when the time stamp of the copied journal
is updated. The recommended interval between time stamps is one second.
Consider the following before setting the interval:
◦
I/O response time slows when time stamps are updating among multiple storage systems.
If you shorten the interval, more time stamps are issued, resulting in an I/O response time
that is slower yet.
◦
If the interval is lengthened, the amount of time that journal data can accumulate increases,
which results in an increased amount of data to be copied.
◦
None of the above is true during the initial copy or resynchronization. During these
operations, lengthening the interval between time stamps does not result in more
accumulated journal data, because data restoring takes place regardless of time stamp.
Planning Cnt Ac-J Z in multiple XP7s using a consistency group
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