ReiserFS is a general-purpose,

journaling file system A journaling file system is a file system that keeps track of changes not yet committed to the file system's main part by recording the goal of such changes in a data structure known as a "journal", which is usually a circular log. In the even ...

initially designed and implemented by a team at

Namesys Namesys was a California corporation responsible for the design and implementation of the ReiserFS and Reiser4 filesystems. It has been inactive since late 2007, and , is listed with the State of California with a status of "Suspended". Owned by H ...

led by

Hans Reiser Hans 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 subseq ...

and licensed under

GPLv2 The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general us ...

. Introduced in version 2.4.1 of the

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 ope ...

, it was the first journaling file system to be included in the standard kernel. ReiserFS was the default file system in

Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi-platform network operating system known as Novell NetWare. Under the lead ...

's SUSE Linux Enterprise until Novell decided to move to

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 extend ...

on October 12, 2006, for future releases. Namesys considered ReiserFS version 3.6 which introduced a new on-disk format allowing bigger filesizes, now occasionally referred to as Reiser3, as stable and feature-complete and, with the exception of security updates and critical bug fixes, ceased development on it to concentrate on its successor,

Reiser4 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. , the Reiser4 patch set is stil ...

. Namesys went out of business in 2008 after Reiser's conviction for murder. The product is now maintained as open source by volunteers. The reiserfsprogs 3.6.27 were released on 25 July 2017. ReiserFS is currently supported on

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

without quota support. It has been discussed for removal from the Linux kernel since early 2022 due to a lack of maintenance upstream, and technical issues inherent to the filesystem, such as the fact it suffers from the

year 2038 problem The year 2038 problem (also known as Y2038, Y2K38, or the Epochalypse) is a time formatting bug in computer systems with representing times after 03:14:07 UTC on 19 January 2038. The problem exists in systems which measure Unix time � ...

; it was deprecated in Linux 5.18, with removal planned for 2025.

Features

At the time of its introduction, ReiserFS offered features that had not been available in existing Linux file systems. One example is tail packing—a scheme to reduce

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 ...

. Tail packing can have a significant performance impact. Reiser4 may have improved this by packing tails where it does not negatively affect performance.

Design

ReiserFS stores file metadata ("stat items"),

directory 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 u ...

entries ("directory items"),

inode The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attribute ...

block lists ("indirect items"), and tails of files ("direct items") in a single, combined

B+ tree A B+ tree is an m-ary tree with a variable but often large number of children per node. A B+ tree consists of a root, internal nodes and leaves. The root may be either a leaf or a node with two or more children. A B+ tree can be viewed as a B- ...

keyed by a universal object ID. Disk blocks allocated to nodes of the tree are "formatted internal blocks". Blocks for leaf nodes (in which items are packed end-to-end) are "formatted leaf blocks". All other blocks are "unformatted blocks" containing file contents. Directory items with too many entries or indirect items which are too long to fit into a node spill over into the right leaf neighbour. Block allocation is tracked by

free space bitmap Free-space bitmaps are one method used to track allocated sectors by some file systems. While the most simplistic design is highly inefficient, advanced or hybrid implementations of free-space bitmaps are used by some modern file systems. Examp ...

s in fixed locations. By contrast,

ext2 The ext2 or second extended file system is a file system for the Linux kernel. It was initially designed by French software developer Rémy Card as a replacement for the extended file system (ext). Having been designed according to the same pr ...

and other Berkeley FFS-like file systems of that time simply used a fixed formula for computing inode locations, hence limiting the number of files they may contain. Most such file systems also store directories as simple lists of entries, which makes directory lookups and updates

linear time In computer science, the time complexity is the computational complexity that describes the amount of computer time it takes to run an algorithm. Time complexity is commonly estimated by counting the number of elementary operations performed by ...

operations and degrades performance on very large directories. The single

design in ReiserFS avoids both of these problems due to better scalability properties.

Performance

Compared with

and

in version 2.4 of the Linux kernel, when dealing with files under 4

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 ...

and with tail packing enabled, ReiserFS may be faster. Before Linux 2.6.33, ReiserFS heavily used the big kernel lock (BKL)—a global kernel-wide lock—which does not scale well for systems with multiple cores,. as the critical code parts are only ever executed by one core at a time.

Usage

ReiserFS was the default file system in SuSE Linux since version 6.4 (released in 2000), until switching to

SUSE Linux Enterprise SUSE Linux Enterprise (often abbreviated to SLE) is a Linux-based operating system developed by SUSE. It is available in two editions, suffixed with Server (SLES) for servers and mainframes, and Desktop (SLED) for workstations and desktop comp ...

10.2 and

openSUSE openSUSE () is a free and open-source software, free and open source RPM Package Manager, RPM-based Linux distribution developed by the openSUSE project. The initial release of the community project was a beta version of SUSE Linux 10.0. Addi ...

11, announced in 2006. Jeff Mahoney of SUSE wrote a post on 14 September 2006 proposing to move from ReiserFS to

for the default installation file system. Some reasons he mentioned were scalability, "performance problems with

extended attributes Extended file attributes are file system features that enable users to associate computer files with metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem (such as permissions or ...

and ACLs", "a small and shrinking development community", and that "

is not an incremental update and requires a reformat, which is unreasonable for most people." On October 4 he wrote a response comment on a blog in order to clear up some issues. He wrote that his proposal for the switch was unrelated to Hans Reiser being under trial for murder. Mahoney wrote he "was concerned that people would make a connection where none existed" and that "the timing is entirely coincidental and the motivation is unrelated."

Criticism

Some directory operations (including (2)) are not

synchronous Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...

on ReiserFS, which can result in data corruption with applications relying heavily on file-based locks (such as mail transfer agents

qmail qmail is a mail transfer agent (MTA) that runs on Unix. It was written, starting December 1995, by Daniel J. Bernstein as a more secure replacement for the popular Sendmail program. Originally license-free software, qmail's source code was ...

and Postfix) if the machine halts before it has synchronized the disk. There are no programs to specifically

defragment In the maintenance of file systems, defragmentation is a process that reduces the degree of file system fragmentation, fragmentation. It does this by physically organizing the contents of the mass storage device used to store computer file, fi ...

a ReiserFS file system, although tools have been written to automatically copy the contents of fragmented files hoping that more contiguous blocks of free space can be found. However, a "repacker" tool was planned for the next Reiser4 file system to deal with file fragmentation. With the rise of

SSD A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is ...

s, this problem became irrelevant.

fsck

The tree rebuild process of ReiserFS's

fsck The system utility fsck (''file system consistency check'') is a tool for checking the consistency of a file system in Unix and Unix-like operating systems, such as Linux, macOS, and FreeBSD. A similar command, CHKDSK, exists in Microsoft Windows ...

has attracted much criticism by the *nix community: If the file system becomes so badly corrupted that its internal tree is unusable, performing a tree rebuild operation may further corrupt existing files or introduce new entries with unexpected contents, but this action is not part of normal operation or a normal file system check and has to be explicitly initiated and confirmed by the administrator. ReiserFS v3 images should not be stored on a ReiserFS v3

partition Partition may refer to: Computing Hardware * Disk partitioning, the division of a hard disk drive * Memory partition, a subdivision of a computer's memory, usually for use by a single job Software * Partition (database), the division of a ...

(e.g. backups or

disk image A disk image, in computing, is a computer file containing the contents and structure of a disk volume or of an entire data storage device, such as a hard disk drive, tape drive, floppy disk, optical disc, or USB flash drive. A disk image is us ...

s for emulators) without transforming them (e.g., by compressing or encrypting) in order to avoid confusing the rebuild. Reformatting an existing ReiserFS v3 partition can also leave behind data that could confuse the rebuild operation and make files from the old system reappear. This also allows malicious users to intentionally store files that will confuse the rebuilder. As the metadata is always in a consistent state after a file system check, ''corruption'' here means that contents of files are merged in unexpected ways with the contained file system's metadata. The ReiserFS successor, Reiser4, fixes this problem.

Earlier issues

ReiserFS in versions of the Linux kernel before 2.4.16 were considered unstable by Namesys and not recommended for production use, especially in conjunction with NFS.ReiserFS download page
see warning. Retrieved 5. July 2006 Early implementations of ReiserFS (prior to that in Linux 2.6.2) were also susceptible to out-of-order write hazards. But the current journaling implementation in ReiserFS is now on par with that of

's "ordered" journaling level.

References

External links

ReiserFS 3.6 at Linus Torvalds' Git repository
– nowadays (2019) the main development resource of ReiserFS 3
ReiserFS and Reiser4 wiki

Reiserfsprogs

convertfs
a utility which performs in-place conversion between any two file systems with sparse file support

– Discussion on ReiserFS fragmentation, including a script for measuring fragmentation and defragmenting files * Windows utilities to access ReiserFS
YAReG – Yet Another R(eiser)FStool GUIrfsd – ReiserDriver
{{File systems 2001 software Disk file systems File systems supported by the Linux kernel