Setting up a Database Availability Group (DAG) in Exchange Server provides complete protection and recovery in the event of a database, network, or server failure. In a DAG, you can have up to 16 Mailbox servers hosting a pool of databases. This helps ensure automatic recovery at the database level in case something happens.
Sometimes situations arise when you need to split a database availability group (DAG) and move mailboxes from one availability group to another. Some common situations are:
- There is a need to separate data due to legal obligations or compliance.
- Data cannot be in other mailboxes due to privacy or data sensitivity.
- It is necessary to merge or divide a part of the company or a sister company. So you have to separate the servers as well.
- There is a huge amount of data on the servers and you need to share the server resources or split the server to reduce the load on the Database Availability Group (DAG).
Due to problems or extreme load, both active copy and passive copy act as active copy, causing a big problem.
Below we will see how to split a Database Availability Group (DAG) in Exchange Server.
The process of splitting a DAG in Exchange Server
The process of splitting an Exchange Server DAG involves adding the databases as active copies on other servers, removing the servers from the current group, and then adding the servers to the new DAG. However, this is easier said than done, as there are all kinds of things that could go wrong.
So, you must first pause the backup on certain databases to ensure full performance of the services during the process.
Let’s take an example (see the image below). You need to split the DAG into two groups where server 1 and server 2 form part of the group and the other servers. The databases must be separated, so database 1 and 2 would be with server 1 and server 2. On the other hand, databases 3 and 4 would be with server 3 and server 4 group.
The first step is to place an active copy of databases 3 and 4 on servers 3 and 4. Once this process is complete, you need to remove the passive copies from servers 1 and 2.
To activate passive copies, open the Exchange Admin Center (EAC) and go to servers > Database. In the details pane, sub Data base Copiesclick Activate.
Alternatively, you can use Move-ActiveMailboxDatabase command (as listed below) in the Exchange Management Shell (EMS).
Move-ActiveMailboxDatabase <database name> -ActivateOnServer <server to activate database on> -MountDialOverride:None
Once this is complete, you should remove the servers you don’t need in the group. To remove a server,
- Open Exchange Admin Center (EAC) and click on servers > Database availability groups.
- Select a DAG and use the minus (-) button to remove a server from the group.
- Then click Save and Close.
You can then create a new Database Availability Group (DAG), add servers 3 and 4 to the group, and then start replication.
Conclude
There are various reasons for splitting a database availability group (DAG) in Exchange Server. If you need to split a DAG, you can follow the above procedure. However, you need to ensure that everything is working well and that there were no problems during the transfer of roles and services. If any problem occurs, it may affect the functionality of the Exchange server or damage the databases. If there are any problems, you can simply rebuild the servers. However, the hard part is data recovery.
For easy data recovery from damaged or corrupted databases, you can take the help of third-party tools like Stellar Repair for Exchange. This tool can repair corrupted databases, with no size limit from any version of Exchange Server, and restore all data. It allows granular export of recovered data to PST and other file formats, such as EML, HTML, PDF and MSG. The tool can also export the recovered data directly to a live Exchange Server of any version. It can handle user mailboxes, user archives, disabled mailboxes, shared mailboxes, and even public folders.