Moving production to Site B after unplanned outages (failover)

For this scenario, assume that an unexpected failure occurs at Site A. The failure at Site A causes the volumes to be suspended or causes a mix of suspended and full duplex volume pairs because the input might have been written to those volumes when the failure occurred.

In a disaster recovery environment, when two storage units are set up in two geographically distinct locations, the storage unit at the production or local site is referred to as Site A, and the storage unit at the remote or recovery site is referred to as Site B.

The failover operation is performed on the storage unit that will become the primary. Production is moved to Site B during this outage, which makes the target volumes at Site B convert to source volumes. The volumes are designated as in a suspended state. Your original source volumes at Site A remain in the state that they were in at the time of the site switch. When Site A is available again, application I/O is switched back from Site B to Site A.

The following steps summarize the actions you must take to move production to Site B as the result of an unplanned outage and then return production to Site A after it recovers.

Perform a failover recovery operation to Site B. After the failover operation has processed successfully, the volumes at Site B transition from target to source volumes.
Mount your target volumes on your server at Site B.
Start your applications on your server at Site B.
After Site A recovers, proceed with the following steps, which are the first steps toward the recovery of the volumes at Site A.
1. Create paths between LSSs at Site B to Site A to allow the volumes at Site A to be synchronized with the Site B volumes.
2. Delete any remote mirror and copy volume relationships that still exist from the source volumes.
3. Wait until the volumes are in full duplex state, and then schedule a time to perform a failback recovery operation using the volumes at Site A. This process resynchronizes the volumes at Site A with the volumes at Site B.
  Note: Failback recovery operations are usually used after a failover recovery has been performed to restart mirroring either in the reverse direction (remote site to local site) or in the original direction (local site to remote site).