Consistency groups and journals

A consistency group is a group of pairs set in primary storage systems and secondary storage systems. By specifying a CTG ID with a BCM or CCI command, you can perform the same operation on all pairs belonging to the CTG in a batch while keeping data consistency.

A master journal is a group of volumes associated with primary storage system. A restore journal is a group of volumes associated with the secondary storage system. If you set each journal as a consistency group and specify a CTG ID, you can use BCM or CCI commands to operate master journal volumes in a master journal, or restore journal volumes in a restore journal in a batch. That is, you can operate volumes for each consistency group while retaining the data update order between the P-VOL and the S-VOL.

Journals are used in Universal Replicator to guarantee data consistency across multiple pairs. Consistency groups are used in other replication software for the same purpose. The same CTG IDs can be used for Universal Replicator and BCM or CCI. Therefore, when you use BCM or CCI, you can perform UR pair tasks using CTG IDs. For Universal Replicator, consistency group IDs specified by BCM or CCI are assigned to journal IDs. If you use Universal Replicator, it is recommended that you specify the same number for a CTG ID and a journal ID. The journal group number can be different in the primary and secondary storage systems.

The number of consistency groups that can be created depends on the storage system model. Following is the maximum number of consistency groups that can be created for P-VOL's consistency group and S-VOL's consistency group combined. The numbers in parenthesis indicate the range of CTG IDs.

• VSP G350, VSP G370, VSP G700, VSP F350, VSP F370, VSP F700: 128 (0 to 127)
• VSP G900, VSP F900: 256 (0 to 255)
• VSP G1x00 and VSP F1500: 256 (0 to 255)