(sometimes incorrectly referred to as data reliability
) in computer data storage
, is a property of some disk arrays
(most commonly in Redundant Arrays of Independent Disks
(RAID) which provides fault tolerance
such that in the case of disk failure
, all or part of the data stored on the array can be recovered. The cost typically associated with providing this feature is a reduction of disk capacity; implementations require either a duplication of the entire data set or an error-correcting code
to be stored on the array.
Redundancy is when the same data values are stored more than once in a table or when the same values are stored in more than one table.