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Reiser4
Developer(s)Namesys
Full nameReiserFS 4
Introduced2004 with Linux
Partition IDsApple_UNIX_SVR2 (Apple Partition Map)
0x83 (MBR)
EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 (GPT)
Structures
Directory contentsDancing B*-tree
Limits
Max file size8TiB on x86
Allowed filename
characters		All bytes except NUL and '/'
Features
Dates recordedmodification (mtime), metadata change (ctime), access (atime)
Date range64-bit timestamps
ForksExtended attributes
File system
permissions		Unix permissions, ACLs and arbitrary security attributes
Transparent
compression		Version 4.1 (beta)
Transparent
encryption		Version 4.1 (beta)
Other
Supported
operating systems		Linux

Reiser4 is a computer file system, a new "from scratch" successor to the ReiserFS file system, developed by Namesys and sponsored by DARPA as well as Linspire.

As of 2006, Reiser4 has not yet been merged into the mainline Linux kernel and consequently is still not supported on many Linux distributions except Linspire, and Arch Linux among a few others; however, its predecessor ReiserFS v3 has been much more widely adopted. Reiser4 is also available from Andrew Morton's -mm kernel sources. Linux kernel developers claim that Reiser4 breaks Linux coding standards, but Hans Reiser suggests political reasons. Namesys has made inclusion into the mainline Linux kernel its first priority.

Features

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; sooner if someone pays them to do so.

Performance

Reiser4 uses B*-trees in conjuction with the dancing tree balancing approach, in which underpopulated nodes won't get 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.

Notes and references

  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 2006-10-13.
  3. Hans Reiser (November 20, 2003). "Benchmarks Of ReiserFS Version 4". Namesys.{{cite web}}: CS1 maint: year (link)

See also

External links

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