[ovirt-users] Use an oVirt-VM as a VDSM server

[Alexander Wels]

On Monday, April 30, 2018 9:02:35 AM EDT James Michels wrote:
> Greetings.
> 
> In terms of teaching our students how to create and configure an oVirt
> infrastructure, we're planning to provide each of them a VM that will act
> as a Manager server, which has no issues so far. The problem is that we
> don't have enough physical machines to use as virtualization servers
> (VDSM), therefore we have been trying to use a CentOS7 based oVirt guest to
> run as a VDSM server.
> 
> However, when trying to add it as a host, a (logical) error message shows
> up saying that the VM doesn't allow virtualization.
> 
> The question is simple: Is there a way to enable virtualization on an oVirt
> VM, so we can deploy them as VDSM servers?
> 
> This is oVirt 4.2.2 FWIW.
> 
> Thanks
> 
> James

James,

Yes its possible, when you install (or re-install) a PHYSICAL host, in the 
host popup dialog there is a kernel tab. Enable 'Nested Virtualization' kernel 
parameter. Once that is enabled and the host is rebooted then you can use VMs 
as VDSM hosts for your setup.

Some gotchas:
- Make sure your cluster cpu type actually matches your physical hosts, if you 
select a wrong one then the exposed CPU options will be wrong and the nested 
virtualization will not work properly.
- You will need to enable mac spoofing for the networking to work correctly.
- VMs running inside a host that is a VM itself will likely have a fairly 
significant performance hit due to the nested virtualization.