Raid spanning : Just makes the computer think alll your hard drives are one big drive, no performance gains
Raid Striping(0): Takes at least 2 drives, and writes "stripes" of data to each drive simultaneously, increasing speed.
Raid Mirroring(1): Takes at least 2 drives, and writes everything twice, once to each drive
Raid 0+1 : Takes 4 drives, gives the speed of striping, and the backup of mirroring, but requires twice the amount of drive space as striping..