Intel Xeon Dual Quad Core 2U Server

Pair multiple identical Drives together to improve Performance or Redundancy.

Mirroring: At least 2 Drives joined as one, data is exactly the same on each one.
For Example if you have 2 - 1TB Hard Drives your computer will only show 1TB, this is designed to protect against data loss. If a drive fails the data is simply read off the other disk.

Striping: At least 2 Identical Drives with data spread across them.
For example, if you have 2 - 1TB Hard Drives it will look like you just have a single 2TB drive. But if you load a file and both of your drives are sending data at 100Mbps each, your total transfer speed will be 200Mbps.