Category: Exchange 2010

Exchange 2010-2016 Database Availability Group (DAG) cluster timeout settings for VMware

Symptom:

Exchange 2010-2016 Database Availability Group (DAG) active database moves between DAG nodes without any reason, when the DAG nodes are VMware Virtual Machines. This may be due to the DAG node being VMotioned by vSphere DRS cluster.

Solution:

The settings below allow you to VMotion without DAG active databases flipping between nodes for no reason.

Although the tip below is mainly useful for Multi-Site DAG clusters, I have seen this flipping happen even within the same site. So, the recommendation is to do these commands on ANY DAG cluster that is running on VMware.

Instructions:

Substitute your DAG name for an example DAG name below, yourDAGname or rpsdag01.

On any Mailbox Role DAG cluster node, open Windows PowerShell with modules loaded.

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Type the following command to check current settings:

cluster /cluster:yourDAGname /prop

Note the following Values:

SameSubnetDelay

SameSubnetThreshold

CrossSubnetDelay

CrossSubnetThreshold

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Type the following commands to change the timeout settings.

cluster /cluster:yourDAGname /prop SameSubnetDelay=2000

cluster /cluster:yourDAGname /prop SameSubnetThreshold=10

cluster /cluster:yourDAGname /prop CrossSubnetDelay=4000

cluster /cluster:yourDAGname /prop CrossSubnetThreshold=10

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Type the command to check that settings took

cluster /cluster:yourDAGname /prop

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You ONLY need to run this on ONE DAG node. It will be replicated to ALL the other DAG nodes.

More Information:

See the article below:

http://technet.microsoft.com/en-us/library/dd197562(v=ws.10).aspx

Enable Microsoft Exchange 2010-2016 DAC mode

Description:

Datacenter Activation Coordination (DAC) mode is a property setting for a database availability group (DAG).

DAC mode is disabled by default and should be enabled for all DAGs with 2 or more members that use continuous replication.

That means the majority of Exchange DAG deployments need the DAC mode.

The DAC is most useful in a multi-datacenter configuration to prevent split brain syndrome, a condition that occurs when all networks fail, and DAG members can’t receive heartbeat signals from each other.

However, I suggest you always enable the DAC.

If you enable the DAC and you need to recover, the recovery takes less commands on the command line. Only the following commandlets will be necessary:

Stop-DatabaseAvailabilityGroup

Restore-DatabaseAvailabilityGroup

Start-DatabaseAvailabilityGroup

Also, if you did NOT enable the DAC, you cannot do so if you have a failure. The DAC must be enabled ahead of time.

Instructions:

Here is how to enable the DAC mode:

1. Go to Exchange Management Shell

2. Type the following, where DAG2 is your DAG name:

Set-DatabaseAvailabilityGroup -Identity DAG2 -DatacenterActivationMode DagOnly

More Information:

For more information, read this article:

http://technet.microsoft.com/en-us/library/dd979790.aspx