The recommendation is to use separate disks for :
- Log files
And this recommendation is even if you only have 1 LUN in the host operating system. You may think that, ”what does it matter, I only have one large SAN as storage”. Well it has to do with Windows. There is only have 1 queue per hard disk (virtual or not) and if you only have 1 hard disk you may end up with waiting for sequential vs random IO operations.