IBM XIV Storage System Copy Services and Migration

If multiple volumes will have dependent write activity, they may be put into a single storagepool in the XIV system and then added to an XIV consistency group to be managed as asingle unit for remote mirroring. Any mirroring actions are taken simultaneously against themirrored consistency group as a whole, preserving dependent write consistency. Mirroringactions cannot be taken against an individual volume pair while it is part of a mirrored CG.However, an individual volume pair may be dynamically removed from the mirroredconsistency group.XIV also supports creation of application-consistent data in the remote mirroring targetvolumes, as discussed 4.5.4, “Creating application-consistent data at both local and theremote sites” on page 109.Defining mirror coupling and peersAfter the remote mirroring targets have been defined, a coupling or mirror may be defined,creating a mirroring relationship between two peers.The two peers in the mirror coupling may be either two volumes (volume peers) or twoconsistency groups (CG peers), as shown in Figure 4-32.SITE 1 SITE 2ProductionDR Test/Recovery ServersVolume PeerDesignatedPrimaryMMMVolumeCoupling/MirrorDefinedVolumeCoupling/MirrorDefinedVolumeCoupling/MirrorDefinedSSSVolume PeerDesignatedSecondaryConsistency Group PeerPrimary Designation (P)Master Role (M)P/MCGCoupling/MirrorDefinedS/SConsistency Group PeerSecondary Designation (S)Slave Role (S)Figure 4-32 Defining mirror couplingEach of the two peers in the mirroring relationship is given a designation and a role. Thedesignation indicates the original or normal function of each of the two peers—either primaryor secondary. The peer designation does not change with operational actions or commands.(If necessary, the peer designation may be changed by explicit user command or action.)The role of a peer indicates its current (perhaps temporary) operational function (eithermaster or slave). The operational role of a peer may change as the result of user commandsor actions. Peer roles typically change during DR testing or a true disaster recovery andproduction site switch.When a mirror coupling is created, the first peer specified (for example, the volumes or CG atsite 1, as shown in Figure 4-32) is the source for data to be replicated to the target system, soit is given the primary designation and the master role.The second peer specified (or automatically created by the XIV system) when the mirroringcoupling is created is the target of data replication, so it is given the secondary designationand the slave role.96 IBM XIV Storage System: Copy Services and Migration