Returning production to Site A after planned and unplanned outages (failback)

Returning production to its original implementation is called a failback recovery. After restoring operations at Site A, you can schedule a failback operation to synchronize data and to enable production to resume at your original site, Site A.

Before you run a failback operation, you must create paths from Site B to Site A between the specific LSSs.

For this scenario, assume that Site A is operational and that connectivity from Site B to Site A is available. Use this procedure to restart your production environment using the volumes from Site B. See Table 1 for an example of the implementation of failover and failback operations.

Note: The process to move production back to your local site (Site A) for a planned outage is identical to the one that is used for an unplanned outage. Therefore, this procedure outlines the steps for both outages.

The failback operation resynchronizes the volumes in the following manner depending on the volume state:

If a volume at Site A is in simplex state, all of the data for that volume is sent from Site B to Site A.
If a volume at Site A is in full-duplex or suspended state and without changed tracks, only the modified data on the volume at Site B is sent to the volume at Site A.
If a volume at Site A is in a suspended state but has tracks that have been modified, the volume at Site B will discover which tracks were modified at any site and send both the tracks that were changed on Site A and the tracks that were marked at Site B from Site A to Site B.

The following assumptions are made for this scenario:

Paths from Site B to Site A are created.
Remote mirror and copy volume pairs are created. Site B volume is the source volume of the failback operation. This volume was initially the target volume of the relationship.

Note: The failback recovery operation can be issued against any remote mirror and copy volume that is in a primary suspended state. The operation copies required data from the source volume to the target volume in order to resume mirroring. Failback recovery operations are usually used after a failover recovery has been issued to restart mirroring either in the reverse direction (remote site to local site) or original direction (local site to remote site). However, this process also works if the target volume is in simplex state.

Perform the following steps using the DS Storage Manager. You can also use the DS CLI to perform Copy Services functions.

Perform a failback recovery operation using volumes at Site B. This process copies all changed tracks from the target volumes back to the source volumes and copies over any tracks that were modified on the original source volumes.
Before returning to normal operation, quiesce your applications (still updating volumes at Site B) to cease all write I/O from updating the source volumes.
Note: On some host systems, such as AIX^®, Windows^®, and Linux^®, before performing FlashCopy operations, you must quiesce your applications that access FlashCopy source volumes. The source volumes must then be unmounted during the FlashCopy establishment. This is to ensure that there is no data in the buffers that could be flushed to the target volumes and potentially corrupt them. Depending on the host operating system, it might be necessary to unmount the source volumes.
From Site A, perform a failover recovery operation using the source volumes. This process converts the full-duplex target volumes at the Site A to suspended source volumes. The volumes at Site A start the change recording process while in failover mode.
Depending on your operating system, it might be necessary to rescan fibre-channel devices and mount the new source volumes at Site A.
From Site A, perform another failback recovery operation using the source volumes. This process resynchronizes the volumes at Site A with volumes at Site B.
Note: Failback recovery operations are usually used after a failover recovery has been issued to restart mirroring either in the reverse direction (remote site to local site) or original direction (local site to remote site).
Mount your volumes at Site A and start your applications on your primary server.