Reiser4 is a

computer A computer is a machine that can be Computer programming, programmed to automatically Execution (computing), carry out sequences of arithmetic or logical operations (''computation''). Modern digital electronic computers can perform generic set ...

file system, successor to the

ReiserFS ReiserFS is a general-purpose, journaling file system initially designed and implemented by a team at Namesys led by Hans Reiser and licensed under GPLv2. Introduced in version 2.4.1 of the Linux kernel, it was the first journaling file syst ...

file system, developed from scratch by Namesys and sponsored by

DARPA The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Adva ...

as well as Linspire. Reiser4 was named after its former lead developer

Hans Reiser Hans Thomas Reiser (born December 19, 1963) is an American computer programmer, entrepreneur, and convicted murderer. In April 2008, Reiser was convicted of the first-degree murder of his wife, Nina Reiser, who disappeared in September 2006. He ...

. , the Reiser4 patch set is still being maintained, but according to

Phoronix Phoronix Test Suite (PTS) is a free and open-source benchmark software for Linux and other operating systems. The Phoronix Test Suite, developed by Michael Larabel and Matthew Tippett, has been endorsed by sites such as Linux.com, LinuxPlanet ...

, it is unlikely to be merged into mainline Linux without corporate backing.

Features

Some of the goals of the Reiser4 file system are: * Atomicity (filesystem operations either complete, or they do not, and they do not corrupt due to partially occurring) * Different transaction models: journaling, write-anywhere (

copy-on-write Copy-on-write (COW), also called implicit sharing or shadowing, is a resource-management technique used in programming to manage shared data efficiently. Instead of copying data right away when multiple programs use it, the same data is shared ...

), hybrid transaction model * More efficient journaling through wandering logs * More efficient support of small files, in terms of disk space and speed through

block suballocation Block suballocation is a feature of some computer file systems which allows large blocks or allocation units to be used while making efficient use of empty space at the end of large files, space which would otherwise be lost for other use to in ...

* Liquid items (or virtual keys) – a special format of records in the storage tree, which completely resolves the problem of

internal fragmentation In computer storage, fragmentation is a phenomenon in the computer system which involves the distribution of data in to smaller pieces which storage space, such as computer memory or a hard drive, is used inefficiently, reducing capacity or perfo ...

* 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: Lempel-Ziv-Oberhumer (LZO),

zlib zlib ( or "zeta-lib", ) is a software library used for data compression as well as a data format. zlib was written by Jean-loup Gailly and Mark Adler and is an abstraction of the DEFLATE compression algorithm used in their gzip file compre ...

* Plugin infrastructure * Dynamically optimized disk-layout through allocate-on-flush (also called delayed allocation in

XFS XFS is a high-performance 64-bit journaling file system created by Silicon Graphics, Inc (SGI) in 1993. It was the default file system in SGI's IRIX operating system starting with its version 5.3. XFS was ported to the Linux kernel in 2001; a ...

) * 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 *

Metadata Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive ...

and inline-data

checksums A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...

* Mirrors and failover * Precise discard support with delayed issuing of discard requests for SSD devices 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 In the maintenance of file systems, defragmentation is a process that reduces the degree of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous ...

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.

Performance

Reiser4 uses

B*-tree In computer science, a B-tree is a self-balancing tree data structure that maintains sorted data and allows searches, sequential access, insertions, and deletions in logarithmic time. The B-tree generalizes the binary search tree, allowing for ...

s 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. , synthetic benchmarks performed by Namesys in 2003 show that Reiser4 is 10 to 15 times faster than its most serious competitor

ext3 ext3, or third extended filesystem, is a journaling file system, journaled file system that is commonly used with the Linux kernel. It used to be the default file system for many popular Linux distributions but generally has been supplanted by ...

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. Other benchmarks from 2006 show results of Reiser4 being slower on many operations. 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 ext4 (fourth extended filesystem) is a journaling file system for Linux, developed as the successor to ext3. ext4 was initially a series of backward-compatible extensions to ext3, many of them originally developed by Cluster File Systems for ...

btrfs Btrfs (pronounced as "better F S", "butter F S", "b-tree F S", or "B.T.R.F.S.") is a computer storage format that combines a file system based on the copy-on-write (COW) principle with a logical volume manager (distinct from Linux's LVM), d ...

and

Integration with Linux

Reiser4 has patches for Linux 2.6, 3.x, 4.x and 5.x., but , Reiser4 has not been merged into the mainline

Linux kernel The Linux kernel is a Free and open-source software, free and open source Unix-like kernel (operating system), kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the k ...

and consequently is still not supported on many

Linux distribution A Linux distribution, often abbreviated as distro, is an operating system that includes the Linux kernel for its kernel functionality. Although the name does not imply product distribution per se, a distro—if distributed on its own—is oft ...

s; however, its predecessor ReiserFS v3 has been widely adopted. Reiser4 is also available from Andrew Morton's -mm kernel sources, and from the Zen patch set. The Linux kernel developers claim that Reiser4 does not follow the Linux "coding style" by the decision to use its own plugin system, but

suggested the decision was made for political reasons. The latest released Reiser4 kernel patches and tools can be downloaded from Reiser4 project page at sourceforge.net.http://reiser4.sourceforge.net/
/ref>

History of Reiser4

Hans Reiser was convicted of

murder Murder is the unlawful killing of another human without justification (jurisprudence), justification or valid excuse (legal), excuse committed with the necessary Intention (criminal law), intention as defined by the law in a specific jurisd ...

on April 28, 2008, leaving the future of Reiser4 uncertain. After his arrest, employees of Namesys were 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; 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, "Commercial activity of Namesys has stopped." Shishkin and others continued the development of Reiser4, making source code available from Shishkin's web site, later relocated to kernel.org. Since 2008, Namesys employees have received 100% of their sponsored funding from

. In 2010,

wrote that Edward Shishkin was exploring options to get Reiser4 merged into Linux kernel mainline. , the file system is still being updated for new kernel releases, but has not been submitted for merging. In 2015, Michael Larabel mentioned it is unlikely to happen without corporate backing, and then he suggested in April 2019 that the main obstacle could be the renaming of Reiser4 to avoid reference to the initial author who was convicted of murder. Shishkin announced a Reiser5 filesystem on December 31, 2019.

References

External links

ReiserFS and Reiser4 wikiCurrent Reiserfs4 patches
as Namesys' website is down
Reiserfs v4 utilitiesIntroduction to Reiser4
on

kuro5hin Kuro5hin (K5; read "corrosion") was a collaborative discussion website founded by Rusty Foster in 1999, having been inspired by Slashdot. Articles were created and submitted by users and submitted to a queue for evaluation. Site members cou ...

Reiser4 transaction design documentTrees in the Reiser4 Filesystem, Part I
from

Linux Journal ''Linux Journal'' (''LJ'') is an American monthly technology magazine originally published by Specialized System Consultants, Inc. (SSC) in Seattle, Washington since 1994. In December 2006 the publisher changed to Belltown Media, Inc. in Hous ...

Trees in the Reiser4 Filesystem, Part II
from

Hans Reiser: The Reiser4 Filesystem

's lecture at

Google Google LLC (, ) is an American multinational corporation and technology company focusing on online advertising, search engine technology, cloud computing, computer software, quantum computing, e-commerce, consumer electronics, and artificial ...

Why Reiser4 is not in the Linux Kernel
at kernelnewbies.org an
Hans Reiser's response to Kernelnewbies' criticismReiser4 and the Politics of the Kernel
by Bruce Byfield on Linux.com

- lecture given by Hans Reiser at

Stanford University Leland Stanford Junior University, commonly referred to as Stanford University, is a Private university, private research university in Stanford, California, United States. It was founded in 1885 by railroad magnate Leland Stanford (the eighth ...