Ever since I'e seen this image, I've always thought of it when it comes to thinking of RAID:
From: [ame]http://www.flickr.com/photos/tirrell/128638167/[/ame]
The water coolers are the drive controllers, and the water bottles are the drives.
RAID-0 gives you extra storage, but no backup ability, like two bottles stacked on top of each other.
RAID-1 mirrors the drives, so if you lose one drive, you have another.
RAID-5 uses three drives, a left drive, a right drive, and a parity drive. As long as you have two of the three drives, your data is safe. 'Tis why I use RAID-5
RAID 0+1 is simpler, it's doubling drives with parity... but unless your drive controller is really stupid, using RAID-5 gives you more space than mirroring.