I recently had a conversation with a colleague concerning high availability (HA) with Exchange 2013 and possible failures of a rack, blade chassis, building or WAN link. The discussion involved placement of the witness server and the number of DAG nodes that would exist in various locations. Since Exchange 2013 and Windows 2012 were released, dynamic quorum has been available in the case multiple voting nodes are down to maintain the availability of Exchange databases.
The following are excellent references for you to plan and decide if Exchange 2013 HA is for you or not.
- Exchange 2013 High Availability & Site Resilience (TechEd Australia 2013/Scott Schnoll)
- Exchange 2013 DAG with Dynamic Quorum (Nuno Mota)
- Windows Server 2012 R2 and Database Availability Groups (Scott Schnoll)
- How Dynamic Quorum keeps Exchange 2013 clusters running during failure (Steve Goodman)
- Exchange 2013 3 node DAG, using failover cluster with dynamic quorum and single global namespace support
- Improving Resilience of Exchange Server 2013 Database Availability Groups with Windows Server 2012 Cluster Dynamic Quorum (Paul Cunningham)
- Windows Server 2012 Failover Clustering Dynamic Quorum for Exchange 2013 DAG