Managing Database Availability Groups

Administrators managing and monitoring a highly available deployment of Exchange Servers need to understand some of the key concepts of DAG. In this section, you are going to learn about DAG, Quorum model, and how to add/remove and modify the members of DAG.

A DAG is a collection of up to 16 mailbox servers built at the top of Windows Failover Cluster. We need to understand the concept of quorum before we create our first DAG.

DAG Quorum model

Cluster quorum has been in use for quite some time now in Windows Failover Cluster and the previous releases of Exchange. It is used to ensure that all or majority of the cluster members have a shared and consistent view of the cluster configuration.

When DAG has an even number of nodes, the quorum that is used is the Node and file share majority. It means an external witness server is used as a tie breaker. Let's take an example of four Exchange 2013/2016 Mailbox servers in DAG where every server gets a vote along...