After a protected object recovers from a fault, failback can switch service provision from the replica object back to the protected object. During this process, the replica object needs to transfer the configuration information and data that changed while the protected object was unavailable back to the protected object to complete data synchronization.
Building a data link
A data link is built between the source cluster and the target cluster through the replication network between the source-side replication service and the target-side replication service. The data link is used to transmit data from the replica object to the protected object.
All replication services register with AOC, and AOC maintains the connection address of each service. You can associate replication services with clusters on the AOC UI. During failback, AOC passes the replication service associated with the source cluster to the target-side replication service as the peer replication service. The target-side replication service periodically checks network connectivity with the source-side replication service. During failback, the target-side service establishes an available data link with the source-side replication service. If the source cluster is associated with multiple replication services, the target-side replication service randomly selects a reachable source-side replication service as the peer replication service and establishes a data link. The target-side replication service can access ABS in the source cluster through the data link.
Obtaining the current state of the replica object
The target-side replication service sends a request to AOC to create a snapshot for the replica object and obtain the metadata of the replica object snapshot. The metadata contains the configuration information of the replica object and the ABS volume snapshot, and records the state of the replica object at that point in time.
Synchronizing the replica object configuration to the protected object
During failover, the replica object may have configuration updates while taking over the protected object and providing services. Therefore, to ensure that the protected object can provide services normally after failback, the target-side replication service sends a request to AOC to synchronize the replica object configuration to the protected object.
Replicating replica object data to the protected object
After the protected object configuration information is synchronized, the snapshot data of the replica object is transmitted to the protected object. The target-side replication service compares fingerprints to identify incremental data of the replica object relative to the protected object, and transmits the data to the protected object.
Creating a restore point on the replica object
After transmitting replica object data to the protected object, the target-side replication service creates a snapshot for the replica object as the restore point of replication and uses it as the replication baseline for subsequent protected object data. If the protected object fails again, you can still execute a failover job to start the replica object from the specified restore point state so that it can take over the protected object and continue providing services.
