Turnover is the process of changing the primary peer in a synchronous replication scheme. The secondary peer becomes the primary peer, and the primary peer becomes the secondary peer. If both peers remain in communication with each other, the protected paths in both peers are read-writable.
Turnover is similar to failover for Asynchronous Replication, but in the case of connected peers in a Synchronous Replication scheme, there is no data loss.
Types of Synchronous Replication Turnover
Graceful Turnover
In this scenario, the roles of the primary and secondary peers are switched, with the secondary peer becoming the primary. Both remain in communication with each other, and the protected paths on both remain read-write accessible.
This is done from the VMS of the secondary peer (the peer that becomes the primary), either using the Web UI or the VCLI.
Ungraceful Turnover
In this scenario, the primary and secondary peers lose contact. As a result, the secondary peer automatically blocks access to the protected path, while the protected path on the primary peer remains read-write. This state remains until the primary peer is explicitly restored to the primary role, even if communication is restored between the peers.
Synchronous Replication Turnover Scenarios
Graceful Turnover
You can perform a graceful turnover between the primary and secondary replication peers if both are in communication with each other (that is, no sync timeout has occurred).
The turnover is performed on the secondary peer (the peer that becomes the primary).
On the secondary peer, perform the turnover by changing the role of the peer to Source. The role of the primary peer changes to secondary. The protected paths on both peers remain accessible for read-write.
On the destination peer, open the Data Protection page and select the Protected Paths tab.
Identify the protected path. The path should be configured for synchronous replication. The state should be "Active" and the role should be "Destination".
Right-click on the protected path to open the Actions menu, and then select Replications/Modify Replication State.
With Primary Synchronous Replication selected, click Turn Over. This will switch the roles of the primary and secondary peers, with the primary peer now becoming the secondary, and the secondary becoming the primary.
Run this VAST CLI command on the secondary peer:
admin> protectedpath modify --modify-replication-state --graceful --id <ID>
where ID is the protected path ID.
Disconnection Between Replication Peers
In the event that communication between the replication peers is lost, the secondary peer automatically blocks access to the protected path. The primary peer automatically changes its role to standalone and maintains read-write access to the protected path.
This occurs on both peers after the sync disconnect timeout period elapses without communication between the peers.
Synchronous Replication Restoration (Failback) Scenarios
Restore After Graceful Turnover
Restore the original roles for the replication peers by changing the role of the secondary peer (originally the primary) to primary. The role of the primary peer (previously the secondary) reverts to secondary. Protected paths on both remain read-write accessible.
On the secondary peer (originally the primary peer, before the turnover), open the Data Protection page and select the Protected Paths tab.
Identify the protected path. The path should be configured for synchronous replication. The state should be "Active" and the role should be "Secondary".
Right-click on the protected path to open the Actions menu, and then select Replications/Modify Replication State.
With Primary Synchronous Replication selected, click Turn Over. This will switch the roles of the primary and secondary peers, with the primary peer (originally the secondary peer) now reverting to the secondary, and the secondary (originally the primary) reverting to the primary.
Run this VAST CLI command on the peer that was originally the primary (the secondary after the turnover):
admin> protectedpath modify --modify-replication-state --graceful --id <ID>
where ID is the protected path ID.
Restore after Resumption of Communication Between Replication Peers
In the event that communication between replication peers is restored, both peers initially remain as unconnected standalone peers.
On the primary peer, change the replication state to now replicate to the secondary peer. This will connect the two peers. Once connected, the protected path on the secondary peer is synchronized to the primary peer. After this, the secondary peer changes state to secondary, and makes access to the protected path read-write.
On the primary peer, open the Data Protection page and select the Protected Paths tab.
Right-click on the protected path, then from the actions menu select Replications/Modify Replication State.
Select Primary Synchronous Replication,
Click Turnover. The role of the peer changes to Primary Synchronous Replication, and that of the secondary peer changes to Secondary Synchronous Replication.
Run this VAST CLI command on the peer that is to become the primary peer:
admin> protectedpath modify --modify-replication-state --graceful --id <ID>
where ID is the protected path ID.