PPRC failover/failback

When production is interrupted by an outage at the primary site, Failover/Failback eliminates the need to transmit all the data back from the recovery site for a full volume copy when the primary site comes back online and is ready to resume production. Following an outage, the primary volumes are often in the same state they were in when the outage occurred. In such a case, the only difference between the primary volumes and the secondary volumes are the updates made to the secondary volumes since the outage occurred.

When an outage occurs, Failover processing causes the secondary volumes to become suspended primary volumes. The Failover PPRC secondary must be in DUPLEX, SUSPENDED, or PENDING-XD state. Any subsequent changes made to those volumes are recorded by the subsystem. When the primary site is capable of resuming production, Failback processing transmits only those changes back to the primary site. The Failover process makes the following assumptions, but operational capabilities may vary and these conditions are not required for the process to function:
  • All paths between the PPRC primary and secondary subsystems are inoperable
  • Paths cannot be used from the secondary subsystem to the primary subsystem
  • The PPRC secondary has updated data consistent with other PPRC secondary volumes
Note:
  • If the device used for failover processing cannot also be used for failback (such as when the storage controller is irreparably damaged and must be replaced), then failback cannot take place and a full volume copy must be executed.
  • If the secondary is in a soft fence state, failback processing clears the soft fence state.