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Mounting a Passive copy of a database in a DAG if the Active copy fails

Posted on 2013-01-30
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Last Modified: 2013-02-01
I have been searching around for a documented procedure for preparing a passive copy of a database in a DAG when the Active database fails. When all is well, its easy to activate a passive copy  but what happens if the server crashes or the database unexpectedly becomes corrupt and dismounts.Most likely the Passive copy will failed/suspended or failed /resynchronizing state and may not mount if all the logs have not been copied over to play back.
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Question by:osiexchange
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by:Simon Butler (Sembee)
Simon Butler (Sembee) earned 125 total points
ID: 38839819
As long as the databases are healthy, and the FSW is available then it should just mount. If you are going in to a suspended/unmounted state then something is wrong with your DAG operation. Many times I have just rebooted the active server and the passive takes over without any interaction from me.

Simon.
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GreatVargas earned 125 total points
ID: 38840148
As Sembee said the behavior is to automatically get the passive copy mounted.. meaning that server will take over the database copy if the server were it's mounted fails.. that's the expected behavior  on a healthy DAG.

also probably you should be aware of two things:

1- Lagges copies
some customers like to have lagged copies to prevent a corruption to replicate over to several database copies (this is a huge discussion topic). just to let you know that if you have a lagged copy of 1 day for example.. meaning that the logs are replicated from the active copy to the lagged copy 1 day after being created.. you need that 1 day of logs to replicate before the other server takes over.. so the bottom line is, dont use lagged copies unless you're under a scenario were you really need to (i.e low bandwith links between the sites)

2- Database Activation Policy
you can prevent database copies from being activated automatically by changing the activation policy at the mailbox server level
http://technet.microsoft.com/en-us/library/dd298046(v=exchg.141).aspx

hope that helps
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