A data storage system comprises a plurality of storage devices and a storage system controller. The storage system controller controls data and redundancy data stored to and read from the storage devices such that the data is stored at least in part in a region which comprises storage areas on least two of the storage devices and such that the storage devices appear as a single storage device to an entity external to the data storage system. The storage system controller comprises a redundancy data generator for generating the redundancy data, a de-duplication fingerprint definer to define a portion of the redundancy data as additionally representing a de-duplication fingerprint for the region, and a data de-duplicator to identify a duplicated region based upon finding a match to the de-duplication fingerprint within the redundancy data of the data storage system.