Embodiments of this application provide a data processing method and a storage system. The method is performed by the storage system, and includes: obtaining physical addresses of a plurality of pieces of first data stored in a hard disk, where each piece of first data is the same as at least one piece of second data in a plurality of pieces of second data written later or to be written; and determining, based on distribution of the physical addresses of the plurality of pieces of first data, to-be-rewritten target first data in the plurality of pieces of first data.