We have a multi-subnet 2 node cluster alwayson setup for a database that's about 1 TB in size for DR purposes in asynchronous mode. 
We have a requirement to failover from primary to secondary and failback to primary after few hours. Can I change the commit mode to synchronous before failing over (similar to the way we can do it for mirroring) and then do the failover when primary and secondary are synchronized? Once it's done, I will have to failover from new primary to old primary. I have tested it on small databases and I was able to do it fine. I just want to make sure because I didn't find this information in Microsoft documentation.

SQL is standalone 2012 SP2 Enterprise

Regards,

Rick

• Edited by Rick818 13 hours 19 minutes ago

Hi Rick,

I am sure when you make fail over data will catch up and become in become sync. 

As you already proved with small size database. you may experience little delay while it catch up. 

Before you do failover from secondary choose the AGname >>rightclick and choose "Show Dashboard"

Check the synchronization State and Failover readyness. Failover ready ness with "No Data Loss" means you can do fail over with out any issues.

I hope this helps you.

Good luck.

kumar

Can I change the commit mode to synchronous before failing over (similar to the way we can do it for mirroring) and then do the failover when primary and secondary are synchronized?

Hi Rick,

You can use the ALTER AVAILABILITY GROUP Transact-SQL statement with the AVAILABILITY_MODE option to change the availability mode. The following example demonstrates that how to change the availability mode to synchronous commit for the AccountsAG availability group.

ALTER AVAILABILITY GROUP AccountsAG MODIFY REPLICA ON ' INSTANCE09 ' WITH

( AVAILABILITY_MODE = SYNCHRONOUS_COMMIT);

And as other post, the most important thing is to make sure that the databases on Primary replica and Secondary replica are synchronized before the failover.

Reference:
Change the Availability Mode of an Availability Replica (SQL Server)
Availability Modes (AlwaysOn Availability Groups)

Thanks,
Lydia Zhang