We've all heard of the ideal 21 disk solution but what is the bare minimum number of seperate physical disks (and don't say 1!!) you can use before performance is severely hindered.

Our Network Admin has just bought a huge new box for a new database (I wasn't involved!) and it has 8 disks. Using RAID for multiplexing means I have just 4 disks available for placement of datafiles. In reality I'll have just 3 as Disk1 will be for system files.

What can I do with 3 disks? Is this still an issue these days now we've got super fast processors? What arguments can I make for us buying additional disks?