HAMMER
| Developer(s) | Matthew Dillon |
|---|---|
| Full name | HAMMER |
| Introduced | July 21, 2008 with DragonFly BSD 2.0[1] |
| Structures | |
| Directory contents | B+ tree[2] |
| Limits | |
| Max. volume size | 1 EiB[2] |
| Features | |
| Forks | No |
| File system permissions | UNIX permissions |
| Transparent compression | Yes[3] |
| Data deduplication | On demand |
| Other | |
| Supported operating systems | DragonFly BSD |
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.[4] HAMMER also supports data block deduplication, meaning that identical data blocks will be stored only once on a file system.[5]
Contents
Features[edit]
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.[4][6][7][8]
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.[6][9][10]
Limitations[edit]
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.[6][8]
Performance[edit]
The following performance-related improvements were introduced on July 2011:[11]
- 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[edit]
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[update], 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.[12] During Google Summer of Code 2013 Daniel Flores implemented compression in HAMMER2 using LZ4 and zlib algorithms.[13] 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.[14]
See also[edit]
References[edit]
- ^ Larabel, Michael (2011-01-07). "Can DragonFlyBSD's HAMMER Compete With Btrfs, ZFS?". Phoronix. Retrieved 2014-05-26.
- ^ a b Dillon, Matthew (2008-06-21). "THE HAMMER FILESYSTEM" (PDF). Retrieved 2009-03-02.
- ^ https://www.phoronix.com/scan.php?page=news_item&px=HAMMER2-LZ4-Default
- ^ a b – DragonFly File Formats Manual
- ^ Sherrill, Justin (2010-11-07). "Deduplication arrives". Retrieved 2011-11-28.
- ^ a b c "HAMMER". DragonFly BSD. Retrieved 2011-11-28.
- ^ Vervloesem, Koen (2010-04-21). "DragonFly BSD 2.6: towards a free clustering operating system". LWN.net. Retrieved 2014-05-26.
- ^ a b George, Siju (May 2014). "Working with Hammer File System and PFSes" (PDF). BSD Magazine. Warsaw, Poland: Hakin9 Media SK. 8 (5): 18–23. Retrieved 2014-05-25.
- ^ – DragonFly System Maintenance and Operation Commands Manual
- ^ Kemp, Juliet (2008-08-04). "Tip of the Trade: Dragonfly BSD and the Hammer Filesystem". ServerWatch. Retrieved 2014-05-26.
- ^ Dillon, Matthew (2011-07-22). "git: HAMMER VFS - Add code to reduce frontend vs flusher locking conflicts". commits (Mailing list).
- ^ Dillon, Matthew (2012-02-08). "DESIGN document for HAMMER2 (08-Feb-2012 update)". users (Mailing list).
- ^ "Block compression feature in HAMMER2". GSoC 2013. Google. Retrieved 2014-06-05.
- ^ "DragonFly Release 3.8". DragonFly BSD. 2014-06-04. Retrieved 2014-06-05.
External links[edit]
- Hammer on the official DragonFly BSD website
- HAMMER2 design document by Matthew Dillon
