Databases that are being replicated within an Exchange Server 2013 database availability group can generally be considered to be either active or passive at any given time.
There are also other states that the database may be in, such as seeding, or due to health problems, but for the purposes of this article we’re going to be looking only at healthy database copies.
The active database copy is the one that is mounted on a DAG member and is being used to serve clients. The passive database copies (up to 15 of them) are those that reside on other mailbox servers within the DAG. Changes are replicated from the active database copy to the passive database copies.
The active database copy can be “moved” between DAG members that host a copy of that database. Although some people consider this to be an actual “move” of the data from one server to the other, in actual fact what is occurring is the active database copy is dismounted, and one of the passive database copies is then mounted.
There are two ways that the active database copy can be moved to another DAG member:
- Failover – this is an unplanned event, such as a failure of the server hosting the active copy
- Switchover – this is a deliberate, administrator-driven event, such as during server maintenance
In this article we’ll look specifically at the database switchover.
Consider a two-member DAG with two databases. Each server hosts one active and one passive database copy.
To move Mailbox Database 1 to E15MB2 we can simply highlight it and then review the status of the database copies. Note that in this case the passive copy on E15MB2 is healthy, with no copy queue length issues and a healthy content index state as well.
Under those conditions we can proceed with the switchover by clicking the link to Activate the database copy.
You’ll be prompted to confirm the action, and then a progress bar let’s you know when the operation is complete.
Click Close when it is finished. In this case we can see that the database is now active on server E15MB2.