About RAIDs

• A RAID (Redundant Array of Inexpensive Disks) is a very expensive (10K$ for cheapo things and up to 500K$ and more for large high-end) container for disks.
• RAIDs support redundancy - i.e. the same data is stored on more then one physical disk, so a single disk failure does not stop I/O.
• RAIDs normally have multiple controllers, for high-availability and for load-balancing. A giant RAID might have 20 such controllers...
• RAIDs allow defining virtual disks, each exposed as a separate LUN, and support LUN masking.
• Finally, mid-range and high-end RAIDs support applications such as taking snapshots of LUNs, remote mirroring, etc.

Originally written by guy keren