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Exchange Server 2010 SP1 DAG

Posted on 2011-10-19
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Last Modified: 2012-05-12
Hi All,
I have 3 node of Exchange Server 2010 SP1 running DAG on Windows Server 2008 R2. I want to testing HA.
1. Shoutdown one node: all Client still can access their mailbox.
2. Shoutdown two node: All Client cannot access their mailbox.

Whether the DAG technology need at lease 2 node is up? Could you guide me?
BR,
Khemarin Set
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Question by:Khemarin
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Expert Comment

by:Radweld
ID: 36998022
Need further information on your exchange design. Were are the nodes geographically and did you configure DAC mode for the dag?
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Author Comment

by:Khemarin
ID: 36998102
3 node is the same subnet and one datacenter. I have 9 database for each server. I haven't configure DAC mode for DAG.

BR,
Khemarin Set
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Accepted Solution

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Akhater earned 2000 total points
ID: 36998152
Hi Khemarin

What you need to know is that, in a DAG, the total number of nodes that are up should be always odd, just like a tennis match :)

If you have 3 nodes 2 out of the 3 should be up.
If you have 5 nodes 3 out of the 5 should be up.
 
etc...

so what you are experiencing is totally normal doesn't matter if it is DAC mode or not and if it is in the same site or not
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Expert Comment

by:Radweld
ID: 36998480
Actually Akhater thats shouldnt be the case. When there are an even number of nodes in a cluster you need a file share witness in order to maintain quorum, if there is no standby FSW then quorum will lost and the cluster will no longer function.

http://technet.microsoft.com/en-us/library/dd298065.aspx

The only other Exchange setting that might inhibit failover is the MaximumActiveDatabases value you assign using the Set-MailboxServer -Server <servername> -MaximumActiveDatabases <numeric> to limit the number of databases that can mount on a single host.

However I suspect your issue is loss of quorum and subsequent failure of the cluster.
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Expert Comment

by:Akhater
ID: 36998486
it is  the case Radweld, when you have an even number of nodes the share witness is to make it odd and it all goes back to what I said.

the share witness is a voter added to the even number of nodes to make it odd that's it

and the failure the OP is experiencing is totally normal
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Author Comment

by:Khemarin
ID: 36998504
The share witness map path my Active Directory. Do you have any more info?
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Expert Comment

by:Akhater
ID: 36998510
What other info do you need? you have an odd number of nodes so you are not using the share witness to start with
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Author Comment

by:Khemarin
ID: 36998564
@Akhater,
 
I just want to verify odd or even, if the node is odd: the configure share witness, it will not working.
If my node is even, my share witness is working, right?

Lastly, if the node is odd, we no need to configure share witness, right? do you have any reference.

BR,
Khemarin
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LVL 49

Expert Comment

by:Akhater
ID: 36998580
Anytime you setup a DAG you have to configure the share witness exchange will automatically decide to use it or not

"if the node is odd: the configure share witness, it will not working."
True it is configured but not used

"If my node is even, my share witness is working, right"
right

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Author Comment

by:Khemarin
ID: 36998623
This is the reason that, when I shoutdown 2 of 3 nodes. The client cannot connection to the mailbox, right? or any reason?

BR,
Khemarin Set
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Expert Comment

by:Akhater
ID: 36998626
when you shutdown 2 nodes out of the 3 you have a loss of quorum and the remaining server will shut the databases down.

If you check the dbs on the remaining server they will be dismounted. this is a normal behavior
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Author Closing Comment

by:Khemarin
ID: 36998636
Thank you for support.
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Expert Comment

by:Akhater
ID: 36998647
My pleasure, thanks for the points
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Expert Comment

by:Radweld
ID: 36998770
"when you shutdown 2 nodes out of the 3 you have a loss of quorum and the remaining server will shut the databases down.

If you check the dbs on the remaining server they will be dismounted. this is a normal behavior"

This is totally incorrect and only the case if you configure DAC mode to prevent split brain.

Normal operation
Normal Operation

Fail 1st Server
Normal Operation
Fail 2nd Server, all databases come active on 3rd Node
Fail 2nd ServerDAG2.JPG
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LVL 49

Expert Comment

by:Akhater
ID: 36998803
Radweld no matter if the DAC is enabled or not Exchange 2010 uses Majority Node Set and it means the N/2+1 of the voters should be online to have quorum.

read http://technet.microsoft.com/en-us/library/dd979799.aspx

Database Availability Group Quorum Modes
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