HAMMER2 is a successor to the HAMMER filesystem, redesigned from the ground up to support enhanced clustering. HAMMER2 supports online and batched deduplication, snapshots, directory entry indexing, multiple mountable filesystem roots, mountable snapshots, a low memory footprint, compression, encryption, zero-detection, data and metadata checksumming, and synchronization to other filesystems or nodes.

Developer(s)Matthew Dillon
Full nameHAMMER2
IntroducedJune 4, 2014 with DragonFly BSD 3.8
File system permissionsUNIX permissions
Transparent compressionYes
Transparent encryptionPlanned
Data deduplicationLive
Supported operating systemsDragonFly BSD


The HAMMER2 file system was conceived by Matthew Dillon, who initially planned to bring it up to minimal working state by July 2012 and ship the final version in 2013.[1][2] During Google Summer of Code 2013 Daniel Flores implemented compression in HAMMER2 using LZ4 and zlib algorithms.[3][4] 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.[5] On October 16, 2017, DragonFly 5.0 was released with bootable support for HAMMER2, though file-system status was marked as experimental.[6]

HAMMER2 had a long incubation and development period before it officially entered production in April 2018, as the recommended root filesystem in the Dragonfly BSD 5.2 release.[7]

Dillon continues to actively develop and maintain HAMMER2 as of December 2018.

See also


  1. Dillon, Matthew (2012-02-08). "DESIGN document for HAMMER2 (08-Feb-2012 update)".
  2. Dillon, Matthew (2011-05-11). "HAMMER2 announcement". users (Mailing list).
  3. "DragonFly BSD 5.0: HAMMER2 a 900 000 procesů".
  4. "Block compression feature in HAMMER2". GSoC 2013. Google. Retrieved 2014-06-05.
  5. "DragonFly Release 3.8". DragonFly BSD. 2014-06-04. Retrieved 2014-06-05.
  6. "DragonFly Release 5.0". DragonFly BSD. 2017-10-16. Retrieved 2017-10-16.
  7. "DragonFly BSD 5.2". Dragonfly BSD Project. 9 April 2018. Retrieved 11 April 2018.
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