[teilo]

Yes, absolutely, because of Microsoft's licensing model for HyperV.

Windows Datacenter Edition is not cost effective for us, and that means we only run two Windows instances per host. By moving MSSQL to Linux, we can free up a Windows Server Standard license for other purposes.

You can run as many non-Windows instances on HyperV as your want, but you can only run 2 Windows instances unless you pay to license every physical core on the server a second or third time, even if you are not using them for Windows (for example, if you wanted to run a third Windows instance on a host.) This means we have additional hardware capacity that we use to run Linux instances next to the 2 allowed Windows instances.

[way0utwest]

Be careful here. I suspect that licensing terms may change a bit with this.

However, you are mistaken. Windows Server standard allows 2 VMs (plus the host). Datacenter allows unlimited VMs. If someone told you otherwise, that's incorrect: http://www.microsoftvolumelicensing.com/ProductResults.aspx?...

[teilo]

No. The licensing terms changed from per socket to per core. Other than that, the rules are the same. If you virtualize Windows Server, you must pay for core licenses for every physical core of the bare metal, regardless of which hypervisor you are using (HyperV, ESX, Xen, etc.). You may then run 2 Windows Server VMs on that host. If you want to run a 3rd, you must relicense every physical core on the machine a second time. You can then run up to 4 Windows Server VMs on that host.

The licensing terms you linked to are for Windows Server VMs. When the licensing documents refer to an "OSE," they are referring to a Windows Server Operating System Environment. They are not referring to other OSs you may be running on the same host (remember, the host can by any hypervisor). Non-Windows VMs are not relevant to Windows licensing, even if you are using HyperV to host them.

The only difference between using HyperV and other hypervisors is: IF you are installing the HyperV role on a Windows Server, and only using it to manage HyperV, you don't have to count that bare-metal Windows Server against your license count, provided you are running Windows Server VMs on that host.

Remember, there is also HyperV Server, which is console-only, and free, but fully functional, and managed just like any other HyperV server. It is a slightly scaled down version of Window Core. You can run as many non-Windows VMs on that as you want, without paying a cent, or pay for Windows VMs according to the above rules.