OK, reality check.

If ALL your AD's are VM's, and for some reason you lose connectivity to your VM's or your VMs are off, you probaby have other machines which are physical that are relying on those AD's to be up.  Therefore it's prudent to mention you may not want to virtualize ALL your AD's. . . . . . .

you can try to do it, but do not destroy phisical server (if you need to use it on-line)

(i'm repeat) is better use dcpromo on new vm.

It's possible that you encounter some network problem: when you convert a phisical system also physical nic will be converted with all network parameters (ip, mask, default gateway etc). At the end of cenversion phase, you need delete old phisical nic (search for hidden device in control panel or via resistry) and assign original ip address in new virtual nic after vmware tool installed.

During this operation the converted dc it will not be able to connect at you ad infrastructure. Some uman error are possible durin this operation, but you can try to do it.

Vmware best practice they say to convert physical server without fsmo roles, but if you are able with microsoft enviroment ... you can reduce migration time.

That's correct that Parker say.... keep one physical active directory server (with a global catalog role).

Bye Alberto

We run domain controllers in virtual machines and have HA configured on ESX cluster.  We have multiple Domain Controllers scatter through different ESX clusters and in case one of the cluster failed, other domain controllers still up and running or even good HA configured will reboot it to other functional ESX host. Always good to have 1-2 physical domain controllers to secure yourself from total storage failured.

"The Power of Knowledge"

So it is a bad idea to convert dc's from physical to virtual correct?

It's a much better idea to stage a new VM and then run dcpromo.  With a new VM you don't have to worry about old device drivers, management software, etc.  If you do clone

1)  You must perform a cold clone.  If you do a hot clone,  when you bring the VM up it will be out of sync.

2)  If you perform a cold clone and then power on the new VM, you must ensure that the old physical server is never powered on again (at least not with network connectivity).

Note also that snapshots are not supported by Microsoft as a valid method for backing up domain controllers.  You'll need to perform a system state backup to be able to properly restore your DC down the road.     Doing so can create inconsistencies accross your AD databases  - support.microsoft.com/kb/888794.