Sorry mate.
RAID is something you'll find written on the box / specs. Its an acronym for 'redundant array of inexpensive disks' but what it really means is '2 smaller capacity disks are often cheaper than 1 huge drive, and can be more resilient too'. RAID techniques vary from keeping a duplicate on the reserve drive to striping across multiple disks. Bear in mind in its common implementations, RAID reduces the storage space by approx 50%, so if you have a 500GB RAID device, it probably only holds 250GB (twice).
The advantage is that if one drive dies, you can put in another and it'll quickly mirror back from the copy without you needing to do anything. Most of the RAID NAS (network attached storage) solutions have 'hot swappable' drives that you can replace in a few seconds if you need to up the storage capacity, or replace a dead disk.
Of course, all of this is lost if its the drive chassis that dies on you. In that case, no amount of new disks will get your data back. For critical data (photos, music, archived PMs, etc
) you might want to read through the detailed specs of a drive to find out what filesystem is being used by the device. If its something that is readable by a normal PC or MAC, you can always whip out the drive and shove it into a tower unit (if you have one). That way, if one drive dies, you're fine. If the device dies, you're fine. If both drives and the device die, well, you're really unlucky.
Does that help?