If SnapMirror encounters any network issues that restrict the operation of synchronous replication, SnapMirror goes into the asynchronous mode.
The source and destination systems communicate with each other continuously. If a network failure disrupts the communication, SnapMirror initiates the following process:
If the latest common Snapshot copy is deleted from the source, SnapMirror does not transition back from asynchronous to synchronous mode. The SnapMirror relationship should be broken and resynchronized, by using the snapmirror break and snapmirror resync commands. However, you can avoid this situation and let the relationship go to synchronous mode automatically, by setting the replication.volume.use_auto_resync option to on. The default value of this option is off.