ABS

ABS is the distributed block storage component of ACOS clusters. It provides storage services for replication objects. At the data layer, a replication object corresponds to one or more volumes in ABS. Synchronous replication of a protected object by the replication service is synchronous replication of volumes.

Synchronous replication uses ABS continuous data protection, which provides the following features:

• Track: Records the areas where writes occur after synchronous replication is enabled.
• Delta Copy: Copies the areas recorded by Track to the target side.
• Mirror: Performs dual writes by immediately synchronizing I/O from the source side to the target side.

When the replication service synchronously replicates a protected object, controller-manager on the replication service first initializes the replica object through a full asynchronous replication job. Then, by using an incremental asynchronous replication job and ABS continuous data protection, controller-manager eventually enables Mirror between the volume on the protected object and the volume on the replica object to start data synchronization.

When failback is required for a protected object, controller-manager of the replication service creates a replica object snapshot through AOC, and then reads the replica object snapshot data from ABS through the RPC protocol. Finally, the data is written to ABS in the source cluster to complete data transmission back to the source.