A good recommendation (and I'd say it's the minimum...) is to have at
least three arrays. One for OS, one for datafiles and one for logfiles.
The swap file can be put on the OS array and so could the tempdb.
Depending on how much your tempdb is being used, you could also gain
some performance by putting this on it's own array(s). In many cases
though this might not be necessary (..but I'm sure a lot of people will
disagree on this...;-)...).
If you backup your databases to a disk on the server, it's also highly
recommended to have this on a separate array.
S *** Schler Persson
Databaseadministrator / Systemadministrator