On-premises Exchange servers are still a thing, and with future versions of Exchange coming on-premises we can assume they still will be for some time to come and on-premises Exchange monitoring is recommended. If your organization still runs on-premises Exchange servers, then Datacenter Activation Coordination (DAC) is a feature you need to understand.

According to Microsoft DAC mode is " used to control the database mount on startup behavior of a DAG. This control is designed to prevent split brain from occurring at the database level during a datacenter switchback. Split brain, also known as split brain syndrome, is a condition that results in a database being mounted as an active copy on two members of the same DAG that are unable to communicate with one another. Split brain is prevented using DAC mode, because DAC mode requires DAG members to obtain permission to mount databases before they can be mounted."

In this blog post I will explain what DAC mode is, how it works, and how it should be used for on-premises Exchange deployments.