This is a little trick that I picked up from an unnamed MSFT person.
Say that you want to have a portable demonstration environment for SCVMM 2012 to show off all of the bells and whistles. You have a limited amount of hardware, say two servers. (maybe even one).
You can install Hyper-V. And you can install SCVMM into a VM. That is all fine and dandy.
You can then install Hyper-V Server into a VM as well. And this looks good until you try to do something that requires the VM within the virtual Hyper-V to power on. Then it falls apart.
Well… you can mix your hypervisors up.
You could install a XenServer within a Hyper-V VM and even create a pool using two or more. They will join and become a Resource Pool.
The key is that you give the XenServer VM a Legacy Network Adapter for installation to proceed.
You can then deploy VMs to the XenServers using SCVMM 2012 (or XenCenter if you like). And the VMs will boot. (yes, all disclaimers apply – a hypervisor in a VM is not a place where you expect anything to be fast, but it can show that something works).
There is also a sneak here as well. Windows VMs will not boot – the reason is that a Windows VM requires an HVM type VM, which requires that the hypervisor in the VM must own the hardware – and it doesn’t. Linux VMs will boot just fine. As they can exist as PV VM’s in XenServer or as HVM type VMs. It is the PV VMs that will boot.
Now, you can always use Hyper-V and install that into a VM running on Hyper-V. I know folks that do that. And these can be managed as well – but none of the VMs can be powered on. So if you need to test SCVMM 2012 and you need to show VM power operations, you need to use Linux VMs running in a virtual XenServer.