By now we are familiar with the concept of DAG. Database availability group is nothing but a set of up to 16 Exchange Server 2016 mailbox servers that provide high availability or automatic database recovery database-level recovery from a database level. It is an improved clustering operation from Exchange Server 2010 onwards. I recommend you to read more about DAG if you are not familiar with, as this article gives only an insight to DAG creation and database copy configuration.

Create Database Availability Group

1. Open Exchange admin center (EAC), and navigate to Servers

2. Click on Database Availability Group on the right pane of the console

3. Click on + sign to add DAG

4. Enter the required information such as DAG Name, Witness Server, Witness directory IP address etc. and click on Save button

Note: If you plan to use a domain controller as witness server, please add it to the Exchange Trusted Subsystem security group. In addition, add the Exchange Trusted Subsystem into the Administrators group

EAC - 1

This will create a Database Availability Group for you Exchange Server 2016 server.

DAG - EAC - 3 1

Add Members to DAG

1. Select the DAG name and click on Manage

2. Save once you add all required servers.

3. Now you can add database for High Availability.

DAG - EAC - 4

Note: The process will take some time, as the failover cluster feature will be installed during the member addition process. Please wait patiently until the operation is finished.

Add Database for High Availability

1. Create Database on one of the DAG Members (follow the usual steps)

2. Select the Database for which you need High Availability, and click on Add database copy from more option.

[Note: You might require to re-login to EMC in case if you did not find the Add database copy option]

3. Follow the wizard and select the server to which you need to replicate the database to.

4. Save the changes, all the required folder and files will be created automatically similar to ver 2010 & 2013.

DAG - EAC - 6

 

DAG - EAC - 7

After the successful addition of database copy, you would be able to see that the database copy on server X1 status is Active Mounted and copy on X2 is Passive Healthy.

Creating the DAG and Adding members to DAG operations are much faster when you use Shell commands, however the through GUI it becomes easy to understand.

I will cover more operation on DBs and DAGs in future posts. Share your suggestions to improve the quality of information.

-Praveen

 

 

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You may see the databases dismounted after you restarted the member server of a DAG (mostly when you only have 2 copies of databases). And if you try to mount the database, it will through the below error.

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Microsoft Exchange Error
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Failed to mount database 'Mailbox Database 0834974974'.
Mailbox Database 0834974974
Failed
Error:
Database 'Mailbox Database 0834974974' can't be mounted on server 'EXH1.exchangedictionary.local' due to a previous error: Failed to determine the mount status of the active database copy. Verify that the underlying cause of the error has been corrected before attempting to mount the database. The error can be ignored and the mount allowed if Mount-Database is reissued with the -Force switch.

Resolution:

As mentioned in the error, it is better try to fix the underlying cause, before you forcefully mount the database.
      • Ensure that the cluster service is up and running
      • Ensure that the DAG members are able to communicate each other, using the replication network (incase if you have replication and MAPI network).
      • Ensure the File Witness is reachable to the server
Mostly, any failure on above checks can lead to this issue, fix the cause and try to mount the database.

Share your feedback.

-Praveen

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