SATA and RAID are two different options for hard drives.
SATA is for the interface, which allows for much faster transfer of data. In other words, if you're going to be playing games from your hard drive- SATA is the way to go.
RAID is for redundancy, meaning for data storage/reliablity. It also speeds up data transfers in certain configurations, not sure which one would suit you (because the data is written to two drives, instead of one, making the seek time lower). You can have both SATA hard drives, and have it setup in a RAID configuration. Just do a google search on RAID, read what you find, and then a google search on SATA, and read what you find. Google is always your friend