How to create an Exchange 2013 Database Availability Group
The first major step in creating an Exchange 2013 DAG is to create the DAG itself. The second procedure is to add databases to the DAG, which will initiate replication and provide the high availability of the DAG technology.
Create Exchange 2013 DAG:
1) Open Exchange Admin Center, click Servers > Database Availability Groups
2) Click the plus sign to create a DAG
3) Specify the following information when prompted:
DAG Name: pick a meaningful name for the DAG. I use either DAG1, or I might use geographic or Datacenter related name like DAG1HQ, if say this DAG is replicating databases within the HQ location.
Witness Server: At this point you need to determine which server will be your primary DAG witness server. The DAG Witness will house a small file share used by the DAG, no resources/load are used on the Witness server by hosting this small DAG file share. For this reason, I recommend the Witness share be placed on a simple file server or utility server (it should never be placed on a DC). Once you have decided on a witness server, you need to go into computer management on the witness server and place the Exchange Trusted Subsystem group into the local administrators group on the Witness Server. Once that is complete you can specify the witness server name in the Witness Server field.
Witness Directory: I generally specify C:\DAG1 for example (or whatever the name of your DAG is)
Database availability group IP addresses: Specify a static IP address that will be used by the DAG. If your Exchange DAG members are in the same subnet, then this is simple and you need to specify an IP address in the same subnet as the Exchange DAG members. If you’re DAG spans multiple subnets then specify one IP in each of the subnets that has DAG members. Note: If you are using a dedicated DAG replication network, I would not put the Witness server IP address in it, I generally place the Witness server IP(s) on the primary LAN.
Next: Click Save to create the DAG.
You now have a Database Availability Group which is a logical location in which to associate your actual DAG replicated database copies which you add in a separate process. Next you need to add database copies to the DAG (this process is what enables the actual DAG replication).