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2 Node DAG Not Working as Expected

Posted on 2011-10-04
Medium Priority
Last Modified: 2012-05-12
A client has a 2 node DAG, with each node in a different AD site and different physical site. Active/Passive sites. Each site also has 1 combined CAS/HUB server. The DAG is in DAC mode (DagOnly). There is some odd behavior in the cluster and we spent a good deal of time trying to figure out the issue. Am I correct in thinking that we should not be able to just move the active database copy to the DR site? We should have to go through the entire Datacenter failover scenario using the cmdlets as defined here: http://technet.microsoft.com/en-us/library/dd351049.aspx

Also, in the cluster resources, I see the primary FSW and the Alternate FSW. Yet, in my lab that I setup to mimick their environment, I only see the primary FSW. Should the alternate FSW be listed in a normal setup?

Question by:vegas588
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Expert Comment

ID: 36909625
A file Share Witness is required for a cluster with an even number of nodes, in the event of a failure of the primary node, the cluster will be left with an odd number and thus an FSW is not required to ensure quorum. In your DAG, the FSW should be in the primary site, with the normally active DAG node.

When DAC mode is enabled, the databases are not supposed to automatically activate in the event of a failure however your are not limited when manually activating a database copy hosted on the other node.  If you are manually activating a copy then this should come live and this is expected behaviour.

Author Comment

ID: 36909920
I'm not sure I understand completely. In their setup, we have no need to use the commands from that article becuase I can activate the databases whenever I want to. This would mean there is no point to all of those commands:

Are you saying that these commands will play no role for them, because that is what i am seeing? If we reboot the primary CAS server or if we reboot the primary DAG Mailbox server, the databaes automatically failover.

Accepted Solution

vegas588 earned 0 total points
ID: 36910746
I was able to clarify the expected behavior from Elan Shudnow's excellent posting on how the quorum works: http://www.shudnow.net/2011/08/05/exchange-2010-site-resilient-dags-and-majority-node-set-clustering-part-1/. Therefore, we can expect to mount databases in the DR site without initiating a complete failover assuming we have only one voter down. However, we know that if we reboot the CAS server in the primary datacenter (which is the Primary FSW), the Databases failover automatically to the DR site. That should not be. We also noticed that in the Failover Cluster Manager, the Alternate FSW is also listed as a Cluster core resource. I have looked at other DAGs and I have not seen this. Any other thoughts on why this automatic failover would occur?

Author Closing Comment

ID: 36941301
partially answered.

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