Exchange Multi Site DAG Failover

Hi We have an Exchange Server 2013 environment which is deployed on 2 Sites.

Site A and Site B. Both Sites are connected via VPN.

We have 2 mailbox servers on each site. We have create a DAG all 4 mailbox server are member of that DAG. We have a third site which is on separate location and this site is also connected via vpn with both Sites as shown in the diagram.

The issue is that our databases were mounted on Mailbox 1 on Site A. Primary active manager was also on Mailbox A. VPN from site B to Site A was disconnected. Due to this our databases were dismounted and users faced disconnectivity. We were able to access Site B from  Site A but Single Site VPN tunnel was disconnected from Site B to Site A. Can anyone help us why our databases were dismounted.

In case our VPN tunnel from Third Site to Site A disconnects then how we can able to failover to Site B. We have DNS failover and if any of our CAS is not accessible then DNS automatically failover to next CAS server and OWA points to active CAS but our DAG does not failover. Can any body give us any opinion.

Any help will be highly appreciated.

Regards,

Anees


  • Edited by AneesUrRehman Friday, July 10, 2015 3:43 PM correction
July 10th, 2015 3:41pm

Ed Crowley,

Thanks for your reply. Our VPN tunnel is very reliable. The thing is that whenever there is any issue with Network connectivity of Site A or Site B, whole site goes down. In this case witness should play it's role and failover to other site. Unfortunately this is not happening in our case. Whenever our Site A goes down site B is not automatically up.Our databases goes down and if  we try to mount database forcefully on Site B we are getting the following error message:

Active Manager isn't reachable on server mbx1.SiteA.com. The Microsoft Exchange Replication service might not be running. Error Error 0x6ba (The RPC server is unavailable) from cli_GetPrimaryActiveManager.
    + CategoryInfo          : InvalidOperation: (ExchangeSite:ADObjectId) [Move-ActiveMailboxDatabase], InvalidOperationException
    + FullyQualifiedErrorId : [Server=MBX2,RequestId=22cee80d-6dbb-4d5a-b21f-84b90e27c1ce,TimeStamp=01/19/2014 5:19:50 AM] [FailureCategory=Cmdlet-InvalidOperationException] 1AAD809E,Microsoft.Exchange.Management.SystemConfigurationTasks.MoveActiveMailboxDatabase
    + PSComputerName        : mbx2.siteB.com

Thank you.

Anees

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July 15th, 2015 7:56am

Hi,

We have 3 Sites now and a witness server on 4th location. How many nodes are required in DAG for each site to automatically failover if a site goes down?

Regards,

Anees

July 30th, 2015 2:30pm

With three sites, you probably don't need the witness in a fourth site.

You must have a majority of nodes able to communicate with each other well for a cluster to stay up.  It's not a matter of how many in a site.  If you only have half the nodes able to communicate well with each other, the file share witness decides which side stays up.

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July 30th, 2015 6:52pm

You are correct that if Site A goes down that Site B should take over. The only reason why it wouldn't is if Site A can still get a hold of the FSW.

In that situation you wouldn't want to force Site B to come online, because it would cause a split brain with Site A.

August 3rd, 2015 6:57pm

Is you DAG enabled with DAC mode. When lets say Site B goes and u have 2 active nodes on that site and 2 active node on Site A so in total u have 4 nodes.

As per Cluster the majority is N/2+1=4/2+1=3

so when Site B goes down  and we have good connectivity with Site C which holds the FSW the nodes on Site B should fail over to Site A because we have the majority ( 2 Node on Site A + FSW)

the reasons why there is no fail over

No proper Permission or connectivity to FSW

Some network issues ( look into app and sys logs) for more issue

Checked for activation Blocks

Look for copy queue lenght and replay queue length

Look for Content index health

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August 4th, 2015 2:44am

Try running Start-DatabaseAvailabilityGroup -Identity DAG1 -ActiveDirectorySite Secondary

Then check if you are able to see the database mounted or mount them

August 4th, 2015 2:50am

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