High Quality Content by WIKIPEDIA articles! HAMMER is a high-availability 64-bit file system developed by Matthew Dillon for DragonFly BSD using B-trees. Its major features include infinite NFS-exportable snapshots, master-multislave operation, configurable history retention, fsckless-mount, and checksums to deal with data corruption. HAMMER also supports data block deduplication — identical data blocks will only be stored once on a file system.