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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 NULL and '/'
Dates recorded modification (mtime), metadata change (ctime), access (atime)
Date range 64-bit timestamps[1]
Forks No
File system permissions Unix permissions
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. Reiser4 was named after its former lead developer Hans Reiser. As of 2015, the Reiser4 patch set is still being maintained, but according to Phoronix, it's unlikely to be merged into mainline Linux without corporate backing.[2]


Some of the goals of the Reiser4 file system are:

  • Different transaction models: Journaling, Write-Anywhere (Copy-on-Write), Hybrid transaction model[3]
  • More efficient journaling through wandering logs
  • More efficient support of small files, in terms of disk space and speed through block suballocation
  • Liquid items (or virtual keys) - a special format of records in the storage tree, which completely resolves the problem of internal fragmentation
  • EOTTL (extents on the twig level) - fully balanced storage tree, meaning that all paths to objects are of equal length
  • Faster handling of directories with large numbers of files
  • Transparent compression (LZO, ZLIB)
  • Plugin infrastructure
  • Dynamically optimized disk-layout through allocate-on-flush (also called delayed allocation in XFS)
  • Delayed actions (tree balancing, compression, block allocation, local defragmentation)
  • R and D (Rare and Dense) caches, synchronized at commit time
  • Transactions support for user-defined integrity
  • Data checksums (currently only for files managed by cryptcompress plugin)
  • Precise discard support[4] with delayed issuing of discard requests for SSD devices[5]

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.[6]


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 in 2003 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.[7] Other benchmarks from 2006 show results of Reiser4 being slower on many operations.[8] Benchmarks conducted in 2013 with Linux Kernel version 3.10 show that Reiser4 is considerably faster in various tests compared to in-kernel filesystems EXT4, btrfs and XFS.[9]

Integration with Linux[edit]

On August 14, 2014, reported that Reiser4 has been ported into the Linux 3.15 kernel, although the latest stable kernel is 3.16.[10] As of 2013, 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,[11] but Hans Reiser suggested political reasons.[12] Latest released reiser4 kernel patches and tools can be downloaded from reiser4 project page at

History of Reiser4[edit]

See also: Hans Reiser

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;[13] 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,[14] making source code available from Shishkin's web site,[15] later relocated to[16] Since 2008, Namesys employees have received 100% of their sponsored funding from DARPA.[17][18][19]

In 2010, Phoronix wrote that Edward Shishkin was exploring options to get Reiser4 merged into Linux kernel mainline.[20] As of 2015, the file system is still being updated for new kernel releases, but has not been submitted for merging. According to Phoronix, it's unlikely to happen without corporate backing.[2]

See also[edit]


  1. ^ Documentation/filesystems/reiser4.txt from a reiser4-patched kernel source, "By default file in reiser4 have 64-bit timestamps."
  2. ^ a b Michael Larabel (23 February 2015). "KDBUS & Other Features You Won't Find In The Linux 4.0 Kernel". Phoronix. 
  3. ^ "Reiser4 transaction models". Reiser4 wiki. 
  4. ^ "PreciseDiscard". Reiser4 wiki. 
  5. ^ "Reiser4 discard support". Reiser4 wiki. 
  6. ^ Reiser, Hans (2004-09-16). "Re: Benchmark: ext3 vs reiser4 and effects of fragmentation.". Namesys, ReiserFS mailing list. Retrieved 2009-10-03. 
  7. ^ Hans Reiser (November 20, 2003). "Benchmarks Of ReiserFS Version 4". Namesys. Retrieved 2014-01-18. 
  8. ^ Justin Piszcz (January 2006). "Benchmarking Filesystems Part II". Retrieved 2006-04-23. 
  9. ^ Michael Larabel (July 31, 2013). "Reiser4 File-System Shows Decent Performance On Linux 3.10". Phoronix. Retrieved 2013-07-31. 
  10. ^ "Reiser4 Now Available For Linux 3.15". Larabel, Michael.
  11. ^ "Linux: Why Reiser4 Is Not in the Kernel". Kerneltrap. September 19, 2005. Archived from the original on 2007-04-23. 
  12. ^ Reiser, Hans (21 July 2006). "The "'official' point of view" expressed by regarding reiser4 inclusion". Retrieved 2008-03-01. 
  13. ^ "Murder Suspect Selling Namesys". Wired News. 2006-12-21. Retrieved 2006-12-30. 
  14. ^ Namesys vanishes, but ReiserFS project lives on. CNet (January 16, 2008). Retrieved on 2008-01-26.
  15. ^ "Namesys things". Retrieved 2010-02-08. 
  16. ^ New location of Namesys software Linux Kernel Mailing List post, 2008-08-04
  17. ^ "Re: we got the DARPA grant to add views to Reiser4". 2004-04-10. Retrieved 2010-02-08. 
  18. ^ "Bug 114785 – reiserfs won't mount with usrquota option". Red Hat Bugzilla. 
  19. ^ "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. 
  20. ^ "Reiser4 May Go For Mainline Inclusion In 2010". 2009-11-10. Retrieved 2010-02-08. 

External links[edit]