Answer:
Data redundancy: Sometime Data redundancy refers to in computer data storage, is a property of some disk arrays which provides fault tolerance, so that all or part of the data stored in the array can be recovered in the case of disk failure. The cost typically associated with providing this feature is a reduction of disk capacity available to the user, since the implementations require either a duplication of the entire data set, or an error-correcting code to be stored on the array.
Redundancy is attained 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.
One of the biggest disadvantages of data redundancy is that it increases the size of the database unnecessarily.