A ShadowImage for Mainframe configuration consists of the following components:
- VSP One Block storage system
- ShadowImage for Mainframe software on the storage system
- Hosts connected to the storage system
- ShadowImage for Mainframe pairs consisting of primary volumes (P-VOLs) and secondary volumes (S-VOLs)
- Consistency groups (CTGs)
Pairs
A volume pair consists of a P-VOL and up to three S-VOLs. Because S-VOLs are updated asynchronously, the P-VOL and its associated S-VOLs might not be identical except immediately after the pair is split. After a pair is split, any further updates to the P-VOL are not copied to the S-VOL. Splitting or deleting a pair allows the host to access the S-VOL.
Consistency groups (CTGs)
If you want to manage multiple ShadowImage for Mainframe pairs as a single group, you can add the pairs to a consistency group (CTG). Consistency groups allow you to perform tasks on all of the pairs in the group at the same time, including splitting pairs and resynchronizing pairs. Performing tasks on a CTG ensures the consistency of the pair status for all pairs in the group.
(VSP One Block 85) When you use a CTG with CCI, you do not need to reserve the CTG.