Developer(s) Matthew Dillon Directory contents B+ tree Forks No | Full name HAMMER Max. volume size 1 EiB | |
Introduced July 21, 2008 with DragonFly BSD 2.0 | ||
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, meaning that identical data blocks will be stored only once on a file system.
Contents
Features
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-filesystems (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 effectively unlimited number of inodes.
Limitations
Currently, 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
The following performance-related improvements were introduced on 000000002011-07-01-0000July 2011:
Development
It was developed specifically for DragonFly BSD to provide a feature-rich yet better designed analogue of then increasingly popular ZFS.
As of June 2014, HAMMER2 file system is actively developed by Matthew Dillon, who initially planned to bring it up to minimal working state by July 2012 and ship the final version in 2013. During Google Summer of Code 2013 Daniel Flores implemented compression in HAMMER2 using LZ4 and zlib algorithms. On June 4, 2014 DragonFly 3.8.0 was released featuring support for HAMMER2, although the file system was said to be not ready for use.