Exchange Server 2013 Database Availability Group (DAG) Installation Guide

Preparing to Deploy an Exchange Server 2013 Database Availability Group

Installing the Mailbox Servers

Database Availability Group members run the Mailbox server role. Although they can also run the Client Access server role this is separate and not required for DAG operations. In some situations the Client Access role should not be installed on the same server, for example:

  • if you plan to use Network Load Balancing for Client Access server high availability (NLB is not supported to co-exist with the Failover Clustering that DAGs leverage)
  • if you have any reason to believe you might later remove the Client Access server role (removal of a single server role is not possible in Exchange Server 2013)

Exchange Server 2013 can run on both Windows Server 2008 R2 and Windows Server 2012. However, due to the dependency on Failover Clustering you should note the following requirements:

  • Windows Server 2008 R2 must be Enterprise edition to support Failover Clustering
  • Windows Server 2012 can be either Standard or Datacenter edition

To install your Exchange Server 2013 DAG members:

  • Install the appropriate pre-requisites for Windows Server 2008 R2 or Windows Server 2012
  • Install Exchange Server 2013 on the servers

In my example scenario I have two servers E15MB1 and E15MB2 both running Windows Server 2012. Each server is installed with both the Client Access and Mailbox server roles. A third server E15FSW exists for the file share witness.



Note: thanks to the concept of “incremental deployment” a DAG can be created using existing mailbox servers that are already in production with active mailboxes on them. There is no hard requirement to build brand new mailbox servers to be able to deploy a DAG.

Configuring Permissions on the File Share Witness

Because the file share witness server is not an Exchange server some additional permissions are required. The Exchange Trusted Subsystem group in Active Directory must be added to the local Administrators group on the server.



The file share witness also requires the File Server feature installed.

PS C:> Add-WindowsFeature FS-FileServer

And you should verify that File and Printer Sharing is allowed through the firewall.



If the file share witness is another Exchange server, such as a Client Access server, it already has the correct permissions configured.

Configuring Networking for Exchange 2013 Database Availability Groups

In this example each server is connected to the network, which is the client-facing network. The two Exchange servers are also connected to the network which will be used for DAG replication traffic.



Dedicated replication networks are not a requirement for Database Availability Groups, however if you do choose to deploy one or more replication networks you must ensure that DNS registration is disabled the network interfaces connected to those networks.



The replication interfaces are also not configured with a default gateway. In the case where replication interfaces for the same replication network are on separate IP subnets, static routes are configured. However in this example that is not required.

The configuration of the network interfaces is important for DAG network auto-config to be successful. For more information see Misconfigured Subnets Appear in Exchange Server 2013 DAG Network.

Configuring Existing Databases

In my example the server E15MB1 and E15MB2 had databases that were automatically created during Exchange 2013 setup. To prepare for database replication within the DAG I performed the following tasks:

  • “Mailbox Database 1″ on E15MB1, which already contains active mailboxes, has been moved from the default folder path onto storage volumes dedicated to databases and transaction log files
  • “Mailbox Database 2″ on E15MB2, which contained no mailboxes, has been removed from Exchange

Those steps may not be required in your environment depending on your existing databases.

Pre-Staging the Cluster Name Object

Depending on your environment the pre-staging of the Cluster Name Object (CNO) may be required (it is a requirement if you are running Windows Server 2012 for the DAG members), but in any case it is a recommended best practice.

The CNO is simply a computer account object in Active Directory. There are two methods you can use to create the CNO.

The first is to manually create the CNO using Active Directory Users & Computers. Create a new computer object with the name that you intend to give to your DAG. Then disable the computer account.



Next, grant the computer account for the first DAG member Full Control permissions for the CNO computer account. Note that you may need to click the View menu in AD Users & Computers and enable Advanced Features before you can see the Security tab for the computer object.



The other method for creating the CNO is to use Michel de Rooij’s Cluster Name Object Pre-Staging script.

Deploying an Exchange Server 2013 Database Availability Group

Creating the Database Availability Group

In the Exchange Admin Center navigate to Servers -> Database Availability Groups and click the + icon to create a new DAG.



Enter the following details for the new Database Availability Group:

  • DAG name – this should match the CNO you pre-staged earlier
  • Witness server – this is required for all DAGs, even those that have an odd number of members and hence run in node majority quorum mode
  • Witness directory – this is optional. If you do not specify a directory Exchange will choose one for you.
  • IP address – the DAG requires an IP address on each IP subnet that is part of the MAPI network. If you do not specify IP addresses the DAG will use DHCP instead.

Click Save when you have entered all of the required details.

Adding Database Availability Group Members

After the DAG has been created it still does not contain any actual members. These need to be added next.

Highlight the new Database Availability Group and click the icon to manage DAG membership.



Add the servers that you wish to join the DAG and then click Save. This process will install and configure the Failover Clustering feature of Windows Server 2012 and add the new DAG members to the cluster.

Note: if you’re using a non-Exchange server for the file share witness, and you have correctly configured the permissions on the FSW, you will still see a warning at this stage that the Exchange Trusted Subsystem is not a member of the local administrators group on the FSW. This is a bug that can be disregarded.



When the operation is complete the Database Availability Group will display the members you added.




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