Why do my DAG databases keep switching servers by themselves?

I have a two-node Exchange 2013 DAG spread across two AD sites. I'm trying to figure out why the databases keep switching between the two servers by themselves. For example, I can activate all databases on Node 1 on a Monday morning. By Tuesday PM a handful of them will have activated themselves on Node 2. I don't get any errors or client downtime. It's an otherwise perfect email system.

I've checked that Activation Preference Number is set correctly on each database and node so either the Active Manager is ignoring this setting or some other problem is causing the switch. The problem is that it causes errors with our backups as they get confused as to which database is active.

I should add that although both servers are in two separate AD sites they are physically in the same rack and connected into the same 1GbE router. They're just on two different subnets.

How do I keep them all activated on Node 1?

May 21st, 2015 4:16am

You need to take a look at the Windows logs and see if Managed Availability is moving them for some reason.  If it is, it should tell you why.
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May 21st, 2015 9:30am

CollectOverMetrics.ps1 will help you figure out why databases moved when they did.
May 21st, 2015 1:41pm

Hi Andy,

Thank you for your question.

Why you active all databases on the same server?

I suggest: if the database belong to Node 1, we active the database on mailbox server of DAG member in Node 1; if the database belong to Node 2, we active the database on mailbox server of DAG member in Node 2. Then we could check if the issue persist.

How do I keep them all activated on Node 1?

A: if the much traffic go Node 1, it will has much delay when we submitted, if the Exchange performance is not very well, mailbox data was submitted over time, the database will keep switching.

We should check if there are any network issue in organization. For example network  flood.

we check there are any error when the DAG database keep switching, and send error to ibsexc@microsoft.com for out troubleshooting.

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim

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May 22nd, 2015 3:44am

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