Reiser4 is a

computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...

file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...

, successor to the ReiserFS 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 A ...

as well as Linspire. Reiser4 was named after its former lead developer Hans Reiser. , 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 which is developed by Michael Larabel and Matthew Tippett. The Phoronix Test Suite has been endorsed by sites such as Linux.com, Linu ...

, 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), sometimes referred to as implicit sharing or shadowing, is a resource-management technique used in computer programming to efficiently implement a "duplicate" or "copy" operation on modifiable resources. If a resource is dupl ...

), 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 inte ...

* 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 which storage space, main storage or secondary storage, is used inefficiently, reducing capacity or performance and often both. The exact consequences of fragmentation depend on the specific ...

* EOTTL (extents on the twig level) – fully balanced storage tree, meaning that all paths to objects are of equal length * Faster handling of

directories Directory may refer to: * Directory (computing), or folder, a file system structure in which to store computer files * Directory (OpenVMS command) * Directory service, a software application for organizing information about a computer network's ...

with large numbers of files * Transparent compression: Lempel-Ziv-Oberhumer (LZO), zlib * 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; as ...

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

and inline-data checksums * 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 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 journaled file system that is commonly used by the Linux kernel. It used to be the default file system for many popular Linux distributions. Stephen Tweedie first revealed that he was working on ext ...

working on files smaller than 1

KiB The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...

. 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 simply by spelling it out) is a computer storage format that combines a file system based on the copy-on-write (COW) principle with a logical volume manager (not to be confused ...

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, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU ...

and consequently is still not supported on many

Linux distribution A Linux distribution (often abbreviated as distro) is an operating system made from a software collection that includes the Linux kernel and, often, a package management system. Linux users usually obtain their operating system by downloading one ...

s; 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, but Hans Reiser suggested political reasons. Latest released reiser4 kernel patches and tools can be downloaded from reiser4 project page at sourceforge.net http://reiser4.sourceforge.net/
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History of Reiser4

Hans Reiser was convicted of

murder Murder is the unlawful killing of another human without justification or valid excuse, especially the unlawful killing of another human with malice aforethought. ("The killing of another person without justification or excuse, especially the ...

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 kernel.org is the main distribution point of source code for the Linux kernel, which is the base of the Linux operating system. Website The website and related infrastructure, which are operated by the Linux Kernel Organization, host the reposi ...

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

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
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 Houston, ...

Trees in the Reiser4 Filesystem, Part II
from

Hans Reiser: The Reiser4 Filesystem
Hans Reiser's lecture at

Google Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...

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 Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is conside ...