Learn the RAID levels and pros/cons. Agree with Essabye it is about IOPs (and latency). You can buy little 4 disk JBOD's with RAID built in for a couple hundred bucks. Also, my buddy was telling me about unraid. They make arrays and offer a free raid sw solution. I have not checked them out, but you may want to look into it if you want a cheap way to learn. If you have any DBA's or Network admins that have been around the block then pick their brains.