Serial Replication Replication task flow - version #0 HMaster Region Server - 0 Client 1.Add Peer Request ZK Cluster Region Server - 1 3.Response 2.Write to ZK Receive watch event and add a new Sync Replication) Replication task flow - version #1 HMaster Region Server - 0 Client 1.Add Peer Request ZK Cluster Region Server - 1 3.Response 2.Write to ZK Receive watch event and add a new ➢ Async zookeeper notification from client to region server. ○ Client does not know whether the peer is added success or failure at server side. ○ Notification lost when RegionServer is not alive. (HBASE-12769)