IBM XIV Storage System Copy Services and Migration

4.4.12 Reactivation, resynchronization, and reverse directionWhen XIV mirroring is reactivated in the reverse direction, as shown in the previous section,changes recorded at the secondary peers are copied to the primary peers. The primary peersmust change the role from master to slave before mirroring can be reactivated in the reversedirection. See Figure 4-40.SITE 1 SITE 2Production ServersDR Test/Recovery ServersRemote TargetVolume PeerDesignated PrimarySlave RoleSVolumeCoupling/MirrorActiveMVolume PeerDesignated SecondaryMaster RoleCG PeerDesignated PrimarySlave RoleSCGCoupling/MirrorActiveMCG PeerDesignated SecondaryMaster RoleFigure 4-40 Reactivation and resynchronizationA typical usage example of this scenario is when returning to the primary site after a truedisaster recovery with production switched to the secondary peers at the remote site.4.4.13 Switching roles of mirrored volumes or CGsWhen mirroring is active and synchronized (consistent), the master and slave roles ofmirrored volumes or consistency groups may be switched simultaneously. Role switching istypical for returning mirroring to the normal direction after changes have been mirrored in thereverse direction after a production site switch. Role switching is also typical for any plannedproduction site switch. For asynchronous mirroring, host server write activity and replicationactivity must be paused very briefly before and during the role switch.4.4.14 Adding a mirrored volume to a mirrored consistency groupFirst make sure that the following constraints are respected:► Volume and CG must be associated with the same pool► Volume is not already part of a CG► Command must be issued only on the master CG► Command must not be run during initialization of volume or CGChapter 4. Remote Mirroring 103