IBM XIV Storage System Copy Services and Migration

4.4.10 Changing role of master volume or CGDuring a true disaster recovery, to resume production at the remote site a slave must have itsrole changed to the master role.In synchronous mirroring, changing a peer role from master to slave allows the slave toaccept mirrored data from the master and cause deletion of metadata that was used to recordany changes while the peer had the master role.In asynchronous mirroring, changing a peer's role automatically reverts the peer to itslast_replicated snapshot. If at any point in time the command is run on the slave (changingthe slave to a master), the former master must first be changed to the slave role (uponrecovery of the primary site) before changing the secondary role back from master to slave.Both peers may temporarily have the master role when a failure at site 1 has resulted in a truedisaster recovery production site switch from site 1 to site 2. When site 1 becomes availableagain and there is a requirement to switch production back to site 1, the production changesmade to the volumes at site 2 must be resynchronized to the volumes at site 1. In order to dothis, the peers at site 1 must change their role from master to slave, as shown in Figure 4-38.SITE 1 SITE 2Production ServersDR Test/Recovery ServersVolume PeerDesignated PrimarySlave RoleSVolumeCoupling/MirrorStandbyMVolume PeerDesignated SecondaryMaster RoleCG PeerDesignated PrimarySlave RoleSCGCoupling/MirrorStandbyMCG PeerDesignated SecondaryMaster RoleFigure 4-38 Changing role to slave volume and CGChapter 4. Remote Mirroring 101