I have a SQL Server 2008 R2 mirror setup running in high safety with automatic failover (synchronous, witness). Over two different nights, the mirror and the primary will be shut down and re-racked. (Mirror on the first night, Primary on the second night)

My original thought is that maybe I should remove the witness prior to shut down so failover would be avoided during/after this process unless I initiated it. But, I’m wondering whether there are any other precautions I should take. The server move should take ~1 hour which is the frequency of log backups as well, so I’m not worried about the transaction log filling on the primary during this time.

Is there any reason to switch from high safety to high performance mode during them move? I’m a little bit unsure of how these modes might behave differently when the mirroring state is DISCONNECTED.

1 Answer 1


I would remove the witness from the session. The reason being that if the 1 online partner (principal) loses communication with the witness, the principal will take itself offline because it has no way to know for sure that the mirror isn't online.

There is no need to change the operating mode. When the principal becomes disconnected, it operates asynchronously. When the mirror reconnects, it will continue to operate asynchronously until they are synchronized, and then it will return automatically to operating synchronously.

  • Thanks, Robert. My concern was, if I left the witness in place, whether something could happen to cause the primary to go offline. I'd like to prevent that possibility so I'll take the witness out of the session to be safe. And, the code is easily scriptable so I can remove/add quickly when the move is done.
    – SandraV
    Jan 7, 2015 at 23:54

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