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.
[7] HAMMER file system provides configurable fine-grained and coarse-grained filesystem histories with online snapshots availability.
Up to 65536 master (read–write) and slave (read-only) pseudo file systems (PFSs), with independent individual retention parameters and inode numbering, may be created for each file system; PFS may be mirrored to multiple slaves both locally or over network connection with near real-time performance.
HAMMER was developed specifically for DragonFly BSD to provide a feature-rich yet better designed analogue[according to whom?]