HP XP P9500 Storage - Manual (Page 11)

The RCU control the secondary storage volume (S-VOL) and the following operations:
•
Journal commands to the MCU.
•
Journal data copy from the master to the restore journal
•
Restore journal data copy to the S-VOL
•
Pair status management and configuration (for example, rejecting write I/Os to the S-VOLs
by way of command rejection or intervention request ).
Pair volumes
Original data is stored in the P-VOL and the remote copy is stored in the S-VOL. The pair can be
paired, split, re-synchronized, and returned to the unpaired (called “simplex”) state. When
synchronized, the volumes are paired; when split, new or changed data sent to the P-VOL is not
copied to the S-VOL. When re-synchronized, changed data is copied to the S-VOL. If a disaster
occurs, production operations can be transferred to the S-VOL. When the primary site is functional
again, operations can be transferred and data can be copied back to the P-VOL.
The P-VOL remains available to the host for read and write I/O operations. The secondary system
rejects write I/Os for the S-VOL by way of command rejection or intervention request, unless the
write-enable option is specified. Then, write I/O is allowed to the S-VOL while the pair is split. In
this instance, S-VOL and P-VOL track maps keep track of differential data and use it to re-synchronize
the pair.
See “Duplicating VOLSERs ” (page 27) for further information on volume requirements and support.
Journal volumes
For Continuous Access Journal Z operations, journal volumes are required on the primary and
secondary systems.
•
Updates to the P-VOL are copied to the master journal volume in the primary system. See the
illustration in
“Journals” (page 11) .
•
Master journal data is copied to the restore journal volume on the secondary system.
•
Journal volumes can have different volume sizes and different RAID configurations.
•
Journal data is stored sequentially and separately in each journal volume in the same journal.
For information on planning journal volumes, see “Sizing journal volumes ” (page 23) .
Journals
Journals help you manage data consistency between multiple P-VOLs and S-VOLs. A journal consists
of two or more data volumes and journal volumes.
You use journals to create multiple pairs and to split, resynchronize, and release multiple pairs.
Journals are required on the primary and secondary systems.
Each data volume and its associated journal volume reside in the same journal.
•
The master journal contains master journal volumes and is associated with the P-VOL.
•
The restore journal contains restore journal volumes and is associated with the S-VOL
Each pair relationship between journals is called a "mirror". A mirror ID identifies a pair relationship
between journals. When the pair is created, it is assigned a mirror ID.
Hardware and software components 11