Managing the Store & DAG: EXCERPT from Microsoft® Exchange Server 2013 Inside Out

Datacenter Activation Coordination

Some DAGs are deployed across data centers in multiple sites. These environments create a specific problem when catastrophic hardware failures occur that knock out a complete data center. Normally, when multiple servers in a DAG are affected, the DAG remains online if quorum can be maintained or stays offline until the majority of the servers are restored to good health and come online again to establish quorum. At this point, Active Manager attempts to restart DAG operations and activate databases to recover from the failure.

Things are a little more complex when a DAG stretches across multiple data centers, especially if the network connections between the two data centers are lost. As the DAG members gradually ...