The Performance Tuning Guidelines for Windows Server 2012 document is available and I’m reviewing and commenting on notable text in it.
The recommendation stays the same. A Hyper-V host is a Hyper-V host, and should not be a domain controller, file server, backup server, DNS server, database server, SBS, etc. Don’t try to get clever with your language – you might think you can out-manoeuvre this but all you’re doing is being stupid and putting your employer/customer(s) at risk.
System administrators should consider carefully what software is installed in the root partition because some software can adversely affect the overall performance of the virtualization server.
The support folks word this more strongly, as they should. Would you really try to install Apache or MySQL on a VMware host (if you could)? And if you wanted to, then you shouldn’t be working in IT, in my opinion.