I've got a an ESX VM and the storage is provided by a decent SAN. On a physical server, I would ordinary install SQL Server across 3 drives; one for the OS + SQL, one for data, and a third for log files. It's a fairly common approach that offers good performance.
However, is there any benefit to this approach when installed on a SAN? If I were to create 3 virtual disks to mirror the physical server approach, I am not going to yield any extra performance because all 3 disks would be drawn from the same SAN, surely?
So what is the best configuration for SQL Server on a VM/SAN?
It depends on how the SAN is setup.
For instance the SAN could be presenting the LUNs/datastores from different disk groups with different performance characteristics and RAID levels. For instance you could have your OS on a R5 10krpm disk-group/LUN/datastore, your Data on a R10 15krpm datastore and your Logs on an SSD-based one.
If you only have one disk-group, LUN and/or datastore then there's unlikely to be any significant performance benefit between the two models but I would still suggest splitting them anyway simply because OS, Data and Logs shouldn't be on the same drive/volume anyway - even if this means being on the same disk-group.
If you can you should do your best to keep at least the Logs on a different disk-group/LUN/datastore for recovery purposes. You could also consider keeping your backups on a different, slower, one too.
In fact re-reading that there's actually no difference between a virtualised and physical MSSQL box in fact.