Microsoft recently announced a new DAG copy activation feature that will be available in Exchange 2016 CU2, but before we talk about that, I’d like to do a quick refresher on how database copy activation works currently and will continue to work for Exchange 2013 and 2010.
The whole point of a Database Availability Group (DAG) is to have multiple copies of a database that are ready to activate in the event of a problem with the server hosting the primary copy. The suggested number of copies for a database is 4, but that depends on your backup strategy and high availability requirements. For the purpose of this article, we’ll use an organization that has four databases each with four copies on four different servers located in two sites. For the sake of the illustration, our databases will be names 1 through 4, and the copies of each database will be designated with a -1 through -4. The primary copy of database 1 will be 1-1, the quaternary (that’s the fancy word for fourth) copy of database 4 will be 4-4. Our database layout is going to look like this