View source for HAMMER (file system)

{{Short description|File system from DragonFly BSD}}
{{Infobox filesystem
| name = HAMMER
| developer = Matthew Dillon
| full_name = HAMMER
| introduction_date = {{Start date and age|2008|07|21}}
| introduction_os = [[Software:DragonFly BSD|DragonFly BSD]] 2.0{{r|lor-2007}}<ref name="phoronix" />
| directory_struct = Modified B+ tree<ref name="hammer-design-doc" />
| max_volume_size = {{nowrap|1 EiB}}<ref name="hammer-design-doc" />
| forks_streams = No
| file_system_permissions = UNIX permissions
| compression = Yes<ref>{{Cite web |title=HAMMER2 File-System Now Uses LZ4 Compression By Default - Phoronix |url=https://www.phoronix.com/scan.php?page=news_item&px=HAMMER2-LZ4-Default |website=www.phoronix.com}}</ref>
| data_deduplication = On demand
| OS = [[Software:DragonFly BSD|DragonFly BSD]]
}}
'''HAMMER''' is a high-availability 64-bit [[File system|file system]] developed by Matthew Dillon for [[Software:DragonFly BSD|DragonFly BSD]] using B+ trees. Its major features include infinite NFS-exportable [[Snapshot (computer storage)|snapshots]], master–multislave operation, configurable history retention, [[Software:Fsck|fsck]]less-mount, and checksums to deal with [[Data corruption|data corruption]].<ref name="man-5-hammer" /> HAMMER also supports data block [[Data deduplication|deduplication]], meaning that identical data blocks will be stored only once on a file system.<ref name="dedup-devblog" /> A successor, [[HAMMER2]], was announced in 2011 and became the default in Dragonfly 5.2 (April 2018).<ref name="hammer2-plan">{{cite mailing list |url=https://www.dragonflybsd.org/mailarchive/kernel/2011-05/msg00010.html |title=HAMMER2 announcement |first=Matthew |last=Dillon |mailing-list=users |date=11 May 2011}}</ref>

== 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 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 [[Mount (computing)|remount]].<ref name="man-5-hammer" /><ref name="descr-page" /><ref name="lwn" /><ref name="bsdmag" />

HAMMER supports volumes up to 1&nbsp;EiB of storage capacity. File system supports [[Cyclic redundancy check|CRC]] checksumming of data and metadata, online layout correction and [[Data deduplication|data deduplication]], and dynamic [[Inode|inode]]s allocation with an effectively unlimited number of inodes.<ref name="descr-page" /><ref name="man-8-hammer" /><ref name="serverwatch" />

== Limitations ==
Currently,{{when|date=May 2020}} regular maintenance is required to keep the file system clean and regain space after file deletions. By default, a [[Software:Cron|cron]] job performs the necessary actions on DragonFly BSD daily. HAMMER does not support multi-master configurations.<ref name="descr-page" /><ref name="bsdmag" />

== Performance ==
HAMMER is optimized to reduce the number of physical I/O operations to cover the most likely path,{{r|kerneltrap-2007}} ensuring [[Sequential access|sequential access]] for optimal performance.

The following performance-related improvements were introduced in {{dts|2011|7||}}:<ref name="ml-2011-07" />
* 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 ==
{{Anchor|HAMMER2}}
HAMMER was developed specifically for DragonFly BSD to provide a feature-rich yet better designed analogue{{According to whom|date=June 2022}} of the then increasingly popular [[ZFS]].

HAMMER was declared production-ready with DragonFly 2.2 in 2009;<ref name="lwn" /> in 2012, design-level work shifted onto [[HAMMER2]], which was declared stable with DragonFly 5.2 in 2018.

{{As of|2019}}, HAMMER is now often referred to as HAMMER1 to avoid confusion with HAMMER2, although an official renaming has not happened. Both filesystems are independent of each other due to different on-disk formats,<ref name="hammer_disk.h">{{cite web |author=Matthew Dillon |date=2017-09-23 |title=hammer_disk.h |url=http://bxr.su/d/sys/vfs/hammer/hammer_disk.h |access-date=2019-03-06 |website=BSD Cross Reference |publisher=[[Software:DragonFly BSD|DragonFly BSD]]}}</ref><ref name="hammer2_disk.h">{{cite web |author=Matthew Dillon |author-link=Matthew Dillon |date=2018-05-05 |title=hammer2_disk.h |url=http://bxr.su/d/sys/vfs/hammer2/hammer2_disk.h |access-date=2019-03-06 |website=BSD Cross Reference |publisher=[[Software:DragonFly BSD|DragonFly BSD]]}}</ref> and continue to receive separate updates and improvements independently.<ref name="4c09d9c4fd910651904ede280ad90a4abf3fc5d7">{{cite mailing list |url=http://lists.dragonflybsd.org/pipermail/commits/2017-March/625653.html |title=git: hammer - HAMMER Version 7 |mailing-list=commits@DragonFly |author=Matthew Dillon |author-link=Matthew Dillon |date=2017-03-27 |access-date=2019-03-06}}</ref>

== See also ==
* [[Software:Comparison of file systems|Comparison of file systems]]
* [[List of file systems]]
* [[HAMMER2]]
* [[ZFS]]
* [[Btrfs]]
* [[Organization:OpenZFS|OpenZFS]]

== References ==
{{Reflist|refs=
<ref name="bsdmag">{{cite journal |last=George |first=Siju |date=May 2014 |title=Working with Hammer File System and PFSes |url=http://bsdmag.org/system/articles/attachment1s/15222/original/BSD_05_2014.pdf |url-status=dead |journal=BSD Magazine |publisher=Hakin9 Media SK |volume=8 |issue=5 |pages=18–23 |archive-url=https://web.archive.org/web/20140527211930/http://bsdmag.org/system/articles/attachment1s/15222/original/BSD_05_2014.pdf |archive-date=27 May 2014 |access-date=2014-05-25 |place=Warsaw, Poland}}</ref>

<ref name="dedup-devblog">{{cite web |last=Sherrill |first=Justin |date=7 November 2010 |title=Deduplication arrives |url=http://www.shiningsilence.com/dbsdlog/2010/11/07/6740.html |access-date=2011-11-28 |archive-date=2011-10-03 |archive-url=https://web.archive.org/web/20111003092020/http://www.shiningsilence.com/dbsdlog/2010/11/07/6740.html |url-status=dead }}</ref>

<ref name="descr-page">{{cite web |title=HAMMER |url=http://www.dragonflybsd.org/hammer/ |access-date=2011-11-28 |work=[[Software:DragonFly BSD|DragonFly BSD]]}}</ref><!--<ref name="gsoc-compression">{{cite web |url=http://www.google-melange.com/gsoc/project/details/google/gsoc2013/iostream/5750892489867264 |title=Block compression feature in HAMMER2 |work=GSoC 2013 |publisher=[[Company:Google|Google]] |access-date=2014-06-05}}</ref>-->

<ref name="hammer-design-doc">{{cite web |last=Dillon |first=Matthew |date=21 June 2008 |title=THE HAMMER FILESYSTEM |url=http://www.dragonflybsd.org/hammer/hammer.pdf |access-date=2009-03-02}}</ref><!--<ref name="hammer-linux">{{cite web |url=http://dlorch.github.com/hammer-linux/ |title=Porting the HAMMER File System to Linux |first=Daniel |last=Lorch |access-date=2011-11-28 }}</ref>-->

<ref name="lwn">{{cite web |last=Vervloesem |first=Koen |date=21 April 2010 |title=DragonFly BSD 2.6: towards a free clustering operating system |url=https://lwn.net/Articles/384200/ |access-date=2014-05-26 |work=LWN.net}}</ref>

<ref name="man-5-hammer">{{man|5|hammer|DragonFly BSD}}</ref>

<ref name="man-8-hammer">{{man|8|hammer|DragonFly BSD}}</ref>

<ref name="ml-2011-07">{{cite mailing list |url=http://leaf.dragonflybsd.org/mailarchive/commits/2011-07/msg00086.html |title=git: HAMMER VFS - Add code to reduce frontend vs flusher locking conflicts |first=Matthew |last=Dillon |mailing-list=commits |date=22 July 2011}}</ref>

<ref name="phoronix">{{cite web |last=Larabel |first=Michael |date=7 January 2011 |title=Can DragonFlyBSD's HAMMER Compete With Btrfs, ZFS? |url=https://www.phoronix.com/scan.php?page=article&item=dragonfly_hammer&num=1 |access-date=2014-05-26 |work=Phoronix}}</ref>

<ref name="serverwatch">{{cite web |last=Kemp |first=Juliet |date=4 August 2008 |title=Tip of the Trade: Dragonfly BSD and the Hammer Filesystem |url=http://www.serverwatch.com/article.php/3763031 |access-date=2014-05-26 |work=ServerWatch}}</ref>

<ref name="lor-2007">{{cite web |date=2007-10-14 |title=В состав DragonFlyBSD 2.0 будет включена файловая система HAMMER |url=https://www.linux.org.ru/news/bsd/2202377 |access-date=2019-08-21 |website=Linux.org.ru |language=ru}}</ref>

<ref name="kerneltrap-2007">{{cite web |author=Jeremy Andrews |date=2007-10-14 |title=HAMMER Performance |url=http://kerneltrap.org/DragonFlyBSD/HAMMER_Performance |archive-url=https://web.archive.org/web/20111104230134/http://kerneltrap.org/DragonFlyBSD/HAMMER_Performance |archive-date=2011-11-04 |access-date=2019-08-21 |website=KernelTrap}}</ref>
}}

== External links ==

{{DragonFly |state=expanded}}
{{File systems |state=expanded}}

[[Category:Distributed file systems]]

{{Sourceattribution|HAMMER (file system)}}