Thou Shall not visualize my SQL Server in a SharePoint Farm.
I have noticed with many clients that use virtualization technologies, that after 8 month to a year or usage , they come back complaining from performance.
I have seen and known about those problems for years but it is a multi faceted issue.
 Infrastructure Decision makers are not the application developers nor the users nor have any experince with the baseline performance of “the application” but only focused on the Disater Recovery ( of disasters that never happen ) ( and if it happens they will never recover from ) . Also they are very focused on uptime of the OS and that is all not even the performance of the OS.
 Not Provisioing the correct virtual resources of the proper types.
SQL Server and his Cousin Mr. Exchange Server like to eat lots of Disk I/O , hence we have to isolate the high frequency Disk io consumers from each other.
 Windows Disk Cache.
 TempDB database location.
 Database storage disk.
 Database Log Storage.
 Backup storage.
With that being said, I am totally for having the SharePoint Web Front End (WFE) servers on virual machines,
performance of IIS on those machines is screaming fast. and will enhance your Fram’s overall performance.
But if you are looking for the real ten commandments click the link.