Spent sometime today clarifying Microsoft’s stance on licensing Windows Servers as virtual machines, this applies regardless of which virtulisatuion platform the VM’s are running on e.g. VMware, Microsoft Virtual Server, Hyper-V.

With standard Windows server licences you have to buy a licence for each VM running Windows Server as the guest OS.

With an enterprise licence you can run up to 4 VM’s under the same license on a single host.

With a datacenter license there is no limit on the number of virtual machines you can run per host.

The enterpise licence is probably going to be the most cost effective for SME’s who have a small number of virtualised servers.

I did ask the question of Microsoft what would happen if you had a pair of VMware ESX servers running 8 Windows VM’s, 4 on each host, using Windows enterprise licences.  One of the ESX hosts fails and the 4 VM’s running on it are then powered up on the remaining host hence having 8 Windows VM’s running under the enterprise licence.  The Microsoft guy said that technically nothing would stop this happening but you would be violating the licensing agreement.

I’ll let you decide what to do a.) Buy expensive datacenter licences or b.) Violate licence agreement whilst your failed host is being repaired, I think I already know most peoples decision.  This same dilemma would also apply in ESX where VM’s could be moving between hosts using vmotion.