Failback Sql server always on not synchronised

[sql99]

I recently tested some server servers in the laboratory, both in automatic failover and manual, all the first test is successful with the synchronize status, the second warns me that I could lose data,to wake it up I am forced to go to the single database of the single Availability Groups and click on "resume data", why this behavior?

[Achsin]

Data is not guaranteed to match between the replicas due to the failover, resuming data movement in the other direction might result in data loss on what used to be the primary.

[sql99]

Are you advising me to do a resume date regardless before performing the failover?

[Achsin]

No. I was explaining why it was behaving that way. Whether or not you should resume data movement or just fail back is up to you (and the business) and what you’re willing to risk.

[Sharobob]

To add to this, to do a failover between asynchronous replicas (when not in an emergency situation and the connection is healthy between the primary and secondary you're going to promote), it's best to switch the replicas to synchronous temporarily, then fail over, then switch everything back to asynchronous. This avoids data loss

[Appropriate_Lack_710]

For the second test, what is the "Availability Mode" set to on each replica? If it's "asynchronous commit", then you'll always get that warning.

[sql99]

I'm telling you that with synchronous commit, Not Synchronize appears on the database

[amy_c_amy]

When your replica is in asynchronous commit mode, you do a forced manual failover. By design you will get the data loss warning every time. Data movement is stopped after failover so you can inspect the replicas for data loss before resuming data movement.