HAMMER (file system)

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. No file system checking is required on remount. HAMMER supports volumes up to 1 EiB of storage capacity. File system supports CRC checksumming of data and metadata, online layout correction and data deduplication, and dynamic inodes allocation with an effectively unlimited number of inodes. == Limitations ==

, regular maintenance is required to keep the file system clean and regain space after file deletions. By default, a cron job performs the necessary actions on DragonFly BSD daily. HAMMER does not support multi-master configurations. == Performance ==

HAMMER is optimized to reduce the number of physical I/O operations to cover the most likely path, ensuring sequential access for optimal performance. The following performance-related improvements were introduced in : • Increased disk read speed in certain scenarios by implementing pulse-width modulated time-domain multiplexer on B-tree cursor operation • Removed a deadlock stalling issue • Improved read performance during heavy, concurrent file write operations == Development ==

HAMMER was developed specifically for DragonFly BSD to "provide a feature-rich yet better designed analogue" of the then increasingly popular ZFS. HAMMER was declared production-ready with DragonFly 2.2 in 2009; and continue to receive separate updates and improvements independently. == See also ==