Hi, The AlwaysOn configuration on SQL 2012 is given below- Two synchronous-commit replicas on Primary data center. Two asynchronous-commit secondary replicas on remote data center. Upgrade steps followed- Step.1- Remove automatic failover on all synchronous-commit replicas. Step.2- Upgrade/update all remote server instances running asynchronous-commit secondary replicas. Step.3- Upgrade/update the local secondary synchronous-commit replicas. Step.4. Manually fail over the availability group to a synchronous-commit secondary replica. Step.5- Upgrade/update the server instance that formerly hosted the primary replica In above steps our application was unable to process the transaction during step.3 when local secondary synchronous-commit replicas was upgrading. I suspect it was because both primary data center node was configured as synchronous-commit and primary server was not able to commit transaction on secondary synchronous-commit replica and wait until secondary replica online after upgrade. In above process I assume that we should change synchronous-commit to asynchronous-commit before upgrading the primary data center replica. Please advise if mine understanding is correct or it is not require to change synchronous-commit to asynchronous-commit during upgrade or patch instance.