InfoScale™ 9.0 Replication Administrator's Guide - AIX

We recommend that you use the fast failback synchronization method. This procedure assumes that the fast failback feature was enabled on the new Primary when takeover was performed. Failing back to the original Primary using fast failback involves the following steps:

1. Converting the original Primary to an acting Secondary, as shown in the vxprint -l rvgname output, and replaying the DCM or SRL of the original Primary to set bits in the DCM of the new Primary. This is performed automatically when the Primary recovers, unless fast failback was disabled during the takeover.

   It is possible that the Primary and Secondary data volumes are not up-to-date because all updates to the original Primary might not have reached the Secondary before the takeover. The failback process takes care of these writes by replaying the SRL or DCM of the original Primary. After the original Primary detects that a takeover has occurred, the new Primary uses information in the DCM or SRL of the original Primary to set bits in its DCM for any blocks that changed on the original Primary before the takeover. You can use the vxrlink status command to monitor the progress of the DCM replay.

2. Converting the original Primary to Secondary and synchronizing the data volumes on the original Primary with the data volumes on the new Primary using the vradmin fbsync command. This command replays the failback log to synchronize the data volumes. The blocks that changed on the original Primary are resynchronized with the new Primary after the DCM of the new Primary is replayed. During the resynchronization, the data from the data volumes on the new Primary is transferred to the data volumes on the original Primary.

   This step is not required if the -autofb option was used at the time of the takeover. The data on the original Primary data volumes is inconsistent for the duration of the replay. To keep a consistent copy of the original Primary data, take a snapshot of the data volumes before starting the replay. When using the vradmin fbsync command, you can also specify the cache or the cachesize option so that a space-optimized snapshot of the original Primary data volumes is automatically created.

3. Migrating the Primary Role back to the original Primary and starting replication.