RAID

RAID (Redundant Array of Independent Disks, Redundant Array of Inexpensive Disks/Drives) is a technique of improving data reliability in the face of possible damage to stored data by storing the data redundantly so it can be recovered if one copy goes bad. Multiple physical drives are used, joined together in one virtual drive so that it appears from the end user standpoint that a file is being stored once on a single drive in a single filesystem, but behind the scenes it is redundantly stored. There are levels from RAID 0 to RAID 6 denoting the methods used, with higher levels generally having greater redundancy and fault-tolerance.

Links

 * Wikipedia article
 * A clean-slate look at disk scrubbing