Hyper-V in Windows Server 2008 Enterprise and Datacenter Edition offers the ability to make virtual machines highly available by leveraging failover clustering. This however is not a good idea in the case of Active Directory Domain Controllers.
This post explain why Hyper-V High Availability for Domain Controllers is not a good idea and how to make Active Directory Domain Controllers highly available in a much easier, more cost effective way.
When combining the Hyper-V Server Role with the Failover Clustering role in Windows Server 2008 you effectively create a High Available solution for virtual machines, stored on shared storage.
In it’s easiest (and most common) form two cluster nodes (“virtual hosts”), installed with Windows Server 2008 (Enterprise or Datacenter Edition), the Hyper-V Server Role and the Failover Clustering Server Role are attached to a shared storage device, where the files for a virtual machine (“virtual guest”) are stored.
One of the cluster nodes (“virtual host”) is the active node and runs the virtual machine (“virtual guest”). The other cluster node (“virtual host”) is the passive node. Both cluster nodes communicate through a heartbeat. That way the passive node can detect when the active node fails and become the active node. This is called a ‘failover’. The failover action can also be triggered manually.