Data redundancy

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Data redundancy (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.