July 13, 2012 at 7:11 am
I am considering scenarios in which we may be placed when using mirroing.
One is after a forced failover, what should we do.
One thing is puzzling me though. After forced service failover, if the old principal comes back up and "if enough log is available", the old principal will rejoin the partnership as a mirror.
I took the part in quotes from MSDN, but what does it mean by "if enough log is available"?
if mirroring is broken due to a partner being down, can i take a tran log backup and effectively break mirroring should the partner come back up, or do the mean something completely different?
July 13, 2012 at 9:17 am
The only thing I can think of that they might mean is if the log file is undamaged and usable to the point that it can be rolled forward. It's an odd statement because the only way that there wouldn't be enough log present is if the log was lost or damaged when the principal was taken offline.
After forcing service, when the principal comes back online, you need to make a decision whether you are okay with the data loss potential. The mirroring session will suspend when the original principal comes back online, and this gives you the opportunity to either drop mirroring and recover the database to manually extract the data that would be lost or to resume mirroring and allow the data to be lost.
Obviously, you only want to force service if you have to.
You can get more info on this in the article I wrote for SQL Server Pro Magazine: Database Mirroring for Disaster Recovery
July 17, 2012 at 12:51 am
If you made a Force failover and if mirroring is active then there will be enough log on the Old principle server. However if you have a force filover and the mirroring is not in sync then there is no questions of enough log availble on the old pronciple server. You need to reconfigure mirroring and then do a failover to make the Old Principle as the current principle server without any data loss.
Thanks
S.R.Kundur
July 17, 2012 at 11:14 am
ksrikanth77 (7/17/2012)
If you made a Force failover and if mirroring is active then there will be enough log on the Old principle server. However if you have a force filover and the mirroring is not in sync then there is no questions of enough log availble on the old pronciple server. You need to reconfigure mirroring and then do a failover to make the Old Principle as the current principle server without any data loss.Thanks
S.R.Kundur
You don't make a lot of sense here. I think you are using words in the wrong context. If I understand what you are saying correctly, then you are correct. I think you are trying to say that if there is not enough log available due to the databases being too far out of sync when service was forced, then you will have to drop and reconfigure mirroring to get it running again. Is this what you are trying to say?:
July 24, 2012 at 8:18 am
ksrikanth77 (7/17/2012)
If you made a Force failover and if mirroring is active then there will be enough log on the Old principle server. However if you have a force filover and the mirroring is not in sync then there is no questions of enough log availble on the old pronciple server. You need to reconfigure mirroring and then do a failover to make the Old Principle as the current principle server without any data loss.Thanks
S.R.Kundur
Hi. Sorry I have not replied on this post, ive just been busy and also forgot!
ksrikanth77, i dont think you understood my question. if i do a forced failover, but both servers are still online, then mirroring is still enabled and so it should be impossible to truncate the log and/or break the log chain. this is why i am unsure what the technet article is trying to say.
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