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Exchange 2010 3 server multi site wan DAG  advice

Posted on 2010-11-24
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Last Modified: 2012-05-10
Hey all, I have been messing with exchange 2010 DAG, tryna work out the ins and outs.

I have the following setup

1 Exchange server A, site A , live users
1 Exchange server B, site B,  live users
1 Exchange server C, site C, no live users

My goal is as follows:

1) setup 3 server DAG, replicate server A to C (active passive) and B to C (active passive) - this part I know how to do
2) make sure that servers NEVER fail over without human intervention, example server A can never dismount its stores without being ordered to do so by a person, server C can never make a passive dbase active without a human order. How do I setup a dag to behave like this?
3) In a 3 server setup for DAG, apparently I do not need the witness server, but initially when I created the DAG with first 2 servers, it made a witness server, how do i get rid of witness server? or will exchange just ignore it?
4)lets say power goes out in exchange site A, I manually bring the dbase online in site C, and users connect to site C and use email. Now power comes back on in site A and exchange server turns on. Will exchange server in site A contact site B and C and see that dbase is active in site C and not mount? or do i risk the split brain thing?


What problems that I do not understand or foresee do I risk with a setup like this?

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Question by:jason_jm
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Akhater earned 2000 total points
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>> 2) make sure that servers NEVER fail over without human intervention, example server A can never dismount its stores without being ordered to do so by a person, server C can never make a passive dbase active without a human order. How do I setup a dag to behave like this?

since each server will be in a different AD site you can do this by running

get-mailboxserver | set-mailboxserver -DatabaseCopyAutoActivationPolicy IntraSiteOnly
this will block a server to active any database that is not in its own AD site

>> 3) In a 3 server setup for DAG, apparently I do not need the witness server, but initially when I created the DAG with first 2 servers, it made a witness server, how do i get rid of witness server? or will exchange just ignore it?
Exchange will ignore it


>>4)lets say power goes out in exchange site A, I manually bring the dbase online in site C, and users connect to site C and use email. Now power comes back on in site A and exchange server turns on. Will exchange server in site A contact site B and C and see that dbase is active in site C and not mount? or do i risk the split brain thing?

To avoid this you have to enable DAC on your DAG by running

Set-DatabaseAvailabilityGroup -Identity DAG01 -DatacenterActivationMode DagOnly

more info at http://technet.microsoft.com/en-us/library/dd979790.aspx
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by:Auric1983
ID: 34212452
Also Jason, when your DAG at Site C comes active, it begins queing up the transaction logs to send back to Site A when it comes back online, and it will only switch back once the logs have been sent and replayed.
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by:Akhater
ID: 34212456
Sorry Auric1983 the DAG will never failback alone however the issue is that the site might go up before the link and lead to split brain if DAC mode is not activated
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by:Auric1983
ID: 34212462
ah! that makes sense,
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by:Auric1983
ID: 34212468

I should know only to open my mouth to change feet... :P

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by:jason_jm
ID: 34280434
to turn them off switches are unrestricted and off
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