Wikipedia:
data redundancy
In computer storage, data redundancy (sometimes incorrectly referred to as data reliability) is a property of some disk arrays (most commonly in RAID arrays) which provides fault tolerance such that if some disks fail, 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.
See also
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