A Random Array of Independent Disks (RAID) is a set of multiple drives put together with the purpose of improving a single drives performance. There are different ways to configure a RAID, each with their its benefits. Some RAID configurations provide a speed boost while others provide data protection in the event of failed drives. Some RAIDs can provide both.
Common RAID Configurations
There are several common RAID configurations. Here is a brief description of each.
RAID 0 turns two or more drives into a faster storage unit. However it provides no security in the event of a drive failure.
RAID 1 takes two drives and creates a mirror, meaning they both have the same information on them. This limits you to the storage space of a single drive but provides you with data protection in case one of the drives fail.
RAID 5 gives you the best of both worlds. Using this configuration you can get the most capacity, speed and protection. The only requirement is that you need to have three drives for it to work. Two drives are dedicated to storage, while the other is dedicated to parity which in the event of a drive failure starts to rebuild the failed drive onto the parity drive.