Method for performing replication control in storage system with aid of relationship tree within database, and associated apparatus

An apparatus for performing replication control in a storage system, the storage system comprising a first storage server and a second storage server, the apparatus comprising:

• a processing circuit, positioned in the first storage server, arranged to control operations of the first storage server, wherein controlling the operations of the first storage server comprises:
• recording relationships between a protection target in the first storage server and a plurality of snapshots of the protection target in a database of the first storage server and updating the database during recording the relationships, wherein the database comprises a relationship tree, and data structure of the relationship tree comprises snapshot nodes respectively corresponding to the plurality of snapshots and a protection target node corresponding to the protection target;
• selecting a non-replicated snapshot that has not been replicated from the first storage server to the second storage server, wherein the plurality of snapshots comprises the non-replicated snapshot, and the non-replicated snapshot is created in the first storage server at a first time point;
• selecting a replicated snapshot that has been replicated from the first storage server to the second storage server as reference of replication difference calculation according to the relationship tree within the database, wherein the plurality of snapshots comprises the replicated snapshot, and the replicated snapshot is created in the first storage server at a second time point prior to the first time point;
• generating snapshot difference data between the non-replicated snapshot and the replicated snapshot, wherein the snapshot difference data indicate any difference between the non-replicated snapshot and the replicated snapshot;
• and
• transmitting the snapshot difference data from the first storage server to the second storage server, to replicate the non-replicated snapshot from the first storage server to the second storage server;
• wherein the step of recording the relationships between the protection target in the first storage server and the plurality of snapshots of the protection target in the database of the first storage server and updating the database during recording the relationships further comprises:
• adding a snapshot node corresponding to the replicated snapshot above the protection target node in the data structure of the relationship tree when the replicated snapshot is created;
• and
• adding a snapshot node corresponding to the non-replicated snapshot above the protection target node in the data structure of the relationship tree when the non-replicated snapshot is created, wherein a parent node of the protection target node is changed from the snapshot node corresponding to the replicated snapshot to the snapshot node corresponding to the non-replicated snapshot.