DeFFS: Duplication-eliminated flash file system

Whenever files are modified, large parts of existing data must get unnecessarily re-written to storage due to the inefficiency on identifying those portions of the files that are actually new in the latest update. The unmodified data are considered as duplicate data since these do not have to be re-written. If NAND flash memory is used for storage, it is beneficial to reduce the duplicate data as many as possible. The issue is how to identify and eliminate the duplicate region efficiently. In this paper, the advanced architecture of flash file system, called duplication-eliminated flash file system, is introduced for duplicate elimination. The important design issues supporting duplicate elimination are how to manage data blocks and how to detect duplicate region. In the DeFFS, index entries of inodes support variable-sized blocks in order to increase the manageability and flexibility of duplicate regions. In addition, DeFFS uses non-overlapping duplicate checking algorithm to reduce the complexity of duplicate checking algorithm. The duplicate elimination can prolong flash memory life cycles by reducing actual amount of page writes, and increase write bandwidth.