A method includes receiving a piece of data for storage in a storage system, breaking the piece of data into a plurality of fixed size data portions, and determining a deduplication hash for each of the fixed size data portions. The method further includes checking for matching hashes already stored in the storage system, storing fixed size data portions unmatched to an already stored hash with metadata identifying the unmatched hash fixed size data portions in the storage system, and storing metadata for hash fixed size data portions already stored in the data storage system. The piece of data is reviewed for further deduplication using sliding window hashes during background activity of the data storage system.