Yes, it takes two drives to create a RAID configuration. Not sure if there is info on here or not, but you might try a search on RAID for the different types.
If not, this should help you get going: http://en.wikipedia.org/wiki/Redunda...ependent_disks
Just be aware.... one type of RAID gives you faster access times by writing a bit to one disk, then the other, so writes/reads are faster... but guess what happens if one drive fails? You guessed it, loss of data.
But it's all on the web to read about. Might want to Google "redundant array of independent drives".