Developer Namesys
Full name Reiser4
Introduced 2004 (Linux)
Partition identifier

Apple_UNIX_SVR2 (Apple Partition Map)
0x83 (MBR)

Basic data partition (GPT)
Directory contents Dancing B*-tree
Max file size 8 TiB on x86
Max filename length 3976 bytes
Allowed characters in filenames All bytes except NUL and '/'
Dates recorded modification (mtime), metadata change (ctime), access (atime)
Date range 64-bit timestamps[1]
Forks Extended attributes
File system permissions Unix permissions, ACLs and arbitrary security attributes
Transparent compression Yes
Transparent encryption No
Data deduplication No
Supported operating systems Linux

Reiser4 is a computer file system, successor to the ReiserFS file system, developed from scratch by Namesys and sponsored by DARPA as well as Linspire. Named after its former lead developer Hans Reiser, Reiser4's continued development is uncertain following his conviction for murder.



Some of the goals of the Reiser4 file system are:

Some of the more advanced Reiser4 features (such as user-defined transactions) are also not available because of a lack of a VFS API for them.

At present Reiser4 lacks a few standard file system features, such as an online repacker (similar to the defragmentation utilities provided with other file systems). The creators of Reiser4 say they will implement these later, or sooner if someone pays them to do so.[2]


Reiser4 uses B*-trees in conjunction with the dancing tree balancing approach, in which underpopulated nodes will not be merged until a flush to disk except under memory pressure or when a transaction completes. Such a system also allows Reiser4 to create files and directories without having to waste time and space through fixed blocks.

As of 2004, synthetic benchmarks performed by Namesys show that Reiser4 is 10 to 15 times faster than its most serious competitor ext3 working on files smaller than 1 KiB. Namesys's benchmarks suggest it is typically twice the performance of ext3 for general-purpose filesystem usage patterns.[3]

Integration with Linux

As of 2011, Reiser4 has not yet been merged into the mainline Linux kernel and consequently is still not supported on many Linux distributions; however, its predecessor ReiserFS v3 has been widely adopted. Reiser4 is also available from Andrew Morton's -mm kernel sources, and from Zen patch set. Linux kernel developers claim that Reiser4 does not follow Linux coding standards,[4] but Hans Reiser suggested political reasons.[5]

History of Reiser4

Hans Reiser was convicted of murder on April 28, 2008, leaving the future of Reiser4 uncertain. After his arrest, employees of Namesys assured they would continue to work and that the events would not slow down the software development in the immediate future. In order to afford increasing legal fees, Hans Reiser announced on December 21, 2006 that he was going to sell Namesys;[6] as of March 26, 2008, it had not been sold, although the website was unavailable. In January 2008, Edward Shishkin, an employee of and programmer for Namesys, was quoted in a CNET interview saying that "Commercial activity of Namesys has stopped." Shishkin and others continued the development of Reiser4,[7] making source code available from Shishkin's web site,[8] later relocated to[9] Since 2008, Namesys employees have received 100% of their sponsored funding from DARPA which is why Edward said 'commercial funding has stopped'.[10][11][12]

Future of Reiser4

Reiser4 development still continues,[13] delivering patches via[14]

In a mailing list post from July 2009, Edward Shishkin wrote that in the coming autumn, they would start exploring the opportunity of getting Reiser4 into the main Linux kernel.[15] In a November 2009 interview[16] with Phoronix he said he was going to publish a plug-in design document for independent expert review. He aimed for January 2011,[17] but as of June 2011, and with the 3.0 Branch of kernel in full development, Reiser4 has not yet been integrated into the mainline kernel.

See also


  1. ^ Documentation/filesystems/reiser4.txt from a reiser4-patched kernel source, "By default file in reiser4 have 64-bit timestamps."
  2. ^ Reiser, Hans (2004-09-16). "Re: Benchmark: ext3 vs reiser4 and effects of fragmentation.". Namesys, ReiserFS mailing list. Retrieved 2009-10-03. 
  3. ^ Hans Reiser (November 20, 2003). "Benchmarks Of ReiserFS Version 4". Namesys. Retrieved 2006-11-28. 
  4. ^ "Linux: Why Reiser4 Is Not in the Kernel". Kerneltrap. September 19, 2005. 
  5. ^ Reiser, Hans (21 July 2006). "The "'official' point of view" expressed by regarding reiser4 inclusion". Retrieved 2008-03-01. 
  6. ^ "Murder Suspect Selling Namesys". Wired News. 2006-12-21.,72342-0.html?tw=wn_technology_1. Retrieved 2006-12-30. 
  7. ^ Namesys vanishes, but ReiserFS project lives on. CNet (January 16, 2008). Retrieved on 2008-01-26.
  8. ^ "Namesys things". Retrieved 2010-02-08. 
  9. ^ New location of Namesys software Linux Kernel Mailing List post, 2008-08-04
  10. ^ "Re: we got the DARPA grant to add views to Reiser4". 2004-04-10. Retrieved 2010-02-08. 
  11. ^
  12. ^ "Reports - ext3 or ReiserFS? Hans Reiser Says Red Hat's Move Is Understandable - Red Hat's Decision is Conservative, Not Radical". LinuxPlanet. Retrieved 2010-02-08. 
  13. ^ ReiserFS Development Mailing List. Retrieved on 2009-04-11.
  14. ^ "Edward Shishkin's Kernel Space". Retrieved 2010-02-08. 
  15. ^ "Edward Shishkin on Reiser4's status". 2009-07-31. Retrieved 2010-02-08. 
  16. ^ "Reiser4 May Go For Mainline Inclusion In 2010". 2009-11-10. Retrieved 2010-02-08. 
  17. ^ Shishkin, Edward (17 Oct 2010). "Re: Mainline inclusion". Retrieved 2010-10-17. 

External links

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