HAMMER
| Developer(s) | Matthew Dillon |
|---|---|
| Full name | HAMMER |
| Introduced | 21 July 2008 with DragonFly BSD 2.0[1] |
| Structures | |
| Directory contents | Modified 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] A successor, HAMMER2, was announced in 2011 and became the default in Dragonfly 5.2 (April 2018).[6]
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 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.[4][7][8][9]
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.[7][10][11]
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.[7][9]
Performance[edit]
The following performance-related improvements were introduced on July 2011:[12]
- 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]
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;[8] in 2012, design-level work has shifted onto HAMMER2, which was declared stable with DragonFly 5.2 in 2018.
As of 2019[update], HAMMER is now often referred to as HAMMER1 to avoid confusion with HAMMER2, although an official renaming hasn't happened. Both filesystems are independent of each other due to different on-disk formats,[13][14] and continue to receive separate updates and improvements independently.[15]
See also[edit]
References[edit]
- ^ Larabel, Michael (7 January 2011). "Can DragonFlyBSD's HAMMER Compete With Btrfs, ZFS?". Phoronix. Retrieved 2014-05-26.
- ^ a b Dillon, Matthew (21 June 2008). "THE HAMMER FILESYSTEM" (PDF). Retrieved 2009-03-02.
- ^ https://www.phoronix.com/scan.php?page=news_item&px=HAMMER2-LZ4-Default
- ^ a b – DragonFly BSD File Formats Manual
- ^ Sherrill, Justin (7 November 2010). "Deduplication arrives". Retrieved 2011-11-28.
- ^ Dillon, Matthew (11 May 2011). "HAMMER2 announcement". users (Mailing list).
- ^ a b c "HAMMER". DragonFly BSD. Retrieved 2011-11-28.
- ^ a b Vervloesem, Koen (21 April 2010). "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. Archived from the original (PDF) on 27 May 2014. Retrieved 2014-05-25.
- ^ – DragonFly BSD System Maintenance and Operation Commands Manual
- ^ Kemp, Juliet (4 August 2008). "Tip of the Trade: Dragonfly BSD and the Hammer Filesystem". ServerWatch. Retrieved 2014-05-26.
- ^ Dillon, Matthew (22 July 2011). "git: HAMMER VFS - Add code to reduce frontend vs flusher locking conflicts". commits (Mailing list).
- ^ Matthew Dillon (2017-09-23). "hammer_disk.h". BSD Cross Reference. DragonFly BSD. Retrieved 2019-03-06.
- ^ Matthew Dillon (2018-05-05). "hammer2_disk.h". BSD Cross Reference. DragonFly BSD. Retrieved 2019-03-06.
- ^ Matthew Dillon (2017-03-27). "git: hammer - HAMMER Version 7". commits@DragonFly (Mailing list). Retrieved 2019-03-06.
External links[edit]
- Hammer on the official DragonFly BSD website
