Raid 0: Your data is distributed over two physical disks (which appears to be one large disk to your system). Offers (near) double speed and huge partitions. But it does have it's price: If one of the disks fails all your data is lost.
Raid 1: All your data is written to both disks. Offers very nice secutity against data loss, since one failed disk may simply be replced, but at the cost of much redundancy (you can only use "half" the space you got).