DC Cloning and Snapshot Restoration

Until now, cloning, snapshotting, copying, or pretty much doing anything but rebuilding from scratch to a virtual domain controller wasn't just unsupported; it had the potential to be really bad for your directory. Cloning or restoring snapshots of DCs could result in USN rollbacks or lingering objects, just to name a couple of problems.

Starting in Windows Server 2012, we now support DC cloning as well as snapshot restoration of domain controllers.

See the complete post at https://blogs.technet.com/b/askpfeplat/archive/2012/10/01/virtual-domain-controller-cloning-in-windows-server-2012.aspx.