There are four main types of RAID, each of which makes tradeoffs between total storage size and redundancy. I used a RAID 5 array, which gave me 1.2 terabytes of storage from five 300-gigabyte disks. At that size, I saved about $550 over an off-the-shelf version. Just plug the drives into a RAID controller, a card that slips into an expansion slot inside your computer, and you´re done. Your Mac, PC or Linux operating system will treat the RAID as a single disk.