June 16, 2011 at 8:45 am
something not clear about database mirroring is getting back to the (original) primary after failover. say for example, you have a catastrophic failure on your primary server and the primary server is out for a week for repairs. when it is brought back online, does mirroring resume automatically such that you can failback to the primary automatically? or must the primary be reloaded again and database mirroring reestablished again from scratch? at what point might they become so out of sync that a full reload/reestablish is necessary?
June 20, 2011 at 12:30 pm
If everything was working nicely up to the point of failover and the original database wasn't disturbed (it didnt need restoring etc) then when mirroring comes back online it should synchronise over time because the log records on the mirror won't be deleted until the sync has occurred. Whether it would be optimal to wait or restore the database and re-establish a mirroring session depends on the volume of data primarily.
I am assuming that you are using a witness or SQL won't detect a quorum and will prevent any updates to either database.
June 21, 2011 at 12:17 am
thanks for the reply, matt. that has clarified the process a lot for me. i guess it depends on the volume of logs and the amount of downtime, whether it is better to resync the mirroring manually or allow the mirroring to resync automatically after bringing up the primary.
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