ReiserFS is a general-purpose, journaled computer file system designed and implemented by a team at Namesys led by Hans Reiser who is referred to as the project's Benevolent Dictator for Life^{[citation needed]}. ReiserFS is currently supported on Linux and may be included in other operating systems in the future. Introduced in version 2.4.1 of the Linux kernel, it was the first journaling file system to be included in the standard kernel. ReiserFS is the default file system on the Slackware, Xandros, Yoper, Linspire, GoboLinux, Kurumin Linux, FTOSX and Libranet Linux distributions. ReiserFS was the default file system in Novell's SUSE Linux Enterprise until Novell decided to move to ext3 on October 12, 2006^[1], two days after principal author Hans Reiser was charged with the murder of his wife. A software developer is a person who is concerned with one or more facets of the software development process, a somewhat broader scope of computer programming or a specialty of project managing. ... Namesys is the company based in the United States and Russia owned and run by Hans Reiser. ... It has been suggested that Criticism of Linux be merged into this article or section. ... In computer engineering, hard disk drive partitioning is the creation of logical divisions upon a hard disk that allows one to apply operating system-specific logical formatting. ... Apple Partition Map (APM) is a partition scheme used to define the low-level organization of data on disks formatted for use with Macintosh computers. ... A Master Boot Record (MBR), or partition sector, is the 512-byte boot sector that is the first sector (Sector 0) of a partitioned data storage device such as a hard disk. ... This article or section may be confusing or unclear for some readers, and should be edited to rectify this. ... GUID Partition Table (GPT) is a standard for the layout of the partition table on a physical hard disk. ... A simple B+ tree example linking the keys 1-7 to data values d1-d7. ... A bit array is an array data structure which compactly stores individual bits (boolean values). ... A tebibyte is a unit of information or computer storage, commonly abbreviated TiB. 1 tebibyte = 240 bytes = 1,099,511,627,776 bytes The tebibyte is closely related to the terabyte, which can either be a synonym for tebibyte, or refer to 1012 bytes = 1,000,000,000,000 bytes... A tebibyte is a unit of information or computer storage, commonly abbreviated TiB. 1 tebibyte = 240 bytes = 1,099,511,627,776 bytes The tebibyte is closely related to the terabyte, which can either be a synonym for tebibyte, or refer to 1012 bytes = 1,000,000,000,000 bytes... December 14 is the 348th day of the year (349th in leap years) in the Gregorian calendar. ... 1901 (MCMI) was a common year starting on Tuesday (link will display calendar) of the Gregorian calendar (or a common year starting on Wednesday of the 13-day-slower Julian calendar). ... January 18 is the 18th day of the year in the Gregorian calendar. ... 2038 (MMXXXVIII) will be a common year starting on Friday of the Gregorian calendar. ... In computing, a fork is additional data associated with a file system object. ... Most modern file systems have methods of administering permissions or access rights to specific users and groups of users. ... In computer security, an access control list (ACL) is a list of permissions attached to an object. ... Filesystem-level encryption, is a form of disk encryption where individual files or directories are encrypted by the file system, in contrast to full disk encryption where the entire partition or disk, where the file system resides, is encrypted. ... An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ... A journaling (or journalling) file system is a file system that logs changes to a journal (usually a circular log in a specially-allocated area) before actually writing them to the main file system. ... A BlueGene supercomputer cabinet. ... In computing, a file system (often also written as filesystem) is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. ... Namesys is the company based in the United States and Russia owned and run by Hans Reiser. ... Company portrait of Hans Reiser Hans Thomas Reiser (born December 1963) is an American computer programmer famous for his contributions to the Free Software community in the field of file systems. ... This article or section does not cite its references or sources. ... It has been suggested that Criticism of Linux be merged into this article or section. ... An operating system (OS) is a set of computer programs that manage the hardware and software resources of a computer. ... The Linux kernel is a Unix-like operating system kernel. ... Slackware was one of the earliest Linux distributions, and is the oldest, and most UNIX-like, distribution still being maintained[1]. It was created by Patrick Volkerding of Slackware Linux, Inc. ... Xandros is both the name of a line of Linux distributions and Xandros Corporation, the company which creates them. ... Yoper running on KDE Desktop. ... This article or section does not cite its references or sources. ... GoboLinux is an alternative Linux distribution. ... Kurumin Linux is a LiveCD Linux distribution based on Debian via Knoppix and Kanotix. ... In computing, Libranet is a Linux distribution that is based on Debian GNU/Linux. ... It has been suggested that Linux be merged into this article or section. ... Novell Inc. ... The ext3 or third extended filesystem is a journalled file system that is commonly used by the Linux operating system. ... October 12 is the 285th day of the year in the Gregorian calendar (286th in leap years). ... For the Manfred Mann album, see 2006 (album). ...

Namesys considers ReiserFS (now occasionally referred to as Reiser3) stable and feature-complete and, with the exception of security updates and critical bug fixes, has thus ceased development on it to concentrate on its successor, Reiser4. 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. ...

A very extensive website can be found at Namesys[5] describing it, with diagrams and detailed explanations of its algorithms and benchmarks.

Features

At the time of its introduction, ReiserFS offered features then unseen in existing Linux file systems:

• Metadata-only journaling (also block journaling, since Linux 2.6.8), its most-publicised advantage over what was the stock Linux file system at the time, ext2.
• Online resizing (growth only), with an underlying volume manager such as LVM. Since then, Namesys has also provided tools to resize (both grow and shrink) ReiserFS file systems offline.
• Tail packing, a scheme to reduce internal fragmentation. Tail packing, however, can have a significant performance impact. Namesys recommends disabling the feature in performance-critical applications. Reiser4 may have improved this by packing tails where it doesn't hurt performance^[2].

Metadata (Greek meta after and Latin data information) are data that describe other data. ... A journaling (or journalling) file system is a file system that logs changes to a journal (usually a circular log in a specially-allocated area) before actually writing them to the main file system. ... The ext2 or second extended file system is a file system for the Linux kernel. ... LVM is an implementation of a logical volume manager for the Linux kernel. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In computer storage, there are three related uses of the term fragmentation: external fragmentation, internal fragmentation, and data fragmentation, all related to storage. ...

Performance

Compared to ext2 and ext3 in version 2.4 of the Linux kernel, when dealing with files under 4 KiB and with tail packing enabled, ReiserFS is often faster by a factor of 10–15.^{[citation needed]} This is of great benefit in Usenet news spools, HTTP caches, mail delivery systems and other applications where performance with small files is critical. The ext2 or second extended file system is a file system for the Linux kernel. ... The ext3 or third extended filesystem is a journalled file system that is commonly used by the Linux operating system. ... According to the International Electrotechnical Commission a kibibyte (a contraction of kilo binary byte) is a unit of information or computer storage. ... Usenet (USEr NETwork) is a global, distributed Internet discussion system that evolved from a general purpose UUCP network of the same name. ...

Criticism

Some directory operations (including unlink(2)) are not synchronous on ReiserFS, which can result in data corruption with applications relying heavily on file-based locks (such as mail transfer agents qmail^[3] and Postfix^[4]) if the machine halts before it has synchronized the disk.^[5] Synchronization (or Sync) is a problem in timekeeping which requires the coordination of events to operate a system in unison. ... A mail transfer agent or MTA (also called a mail transport agent, mail server, or a mail exchanger in the context of the Domain Name System) is a computer program or software agent that transfers electronic mail messages from one computer to another. ... qmail is a mail transfer agent that runs on Unix. ... Postfix is an open source mail transfer agent (MTA), a computer program for the routing and delivery of email, that is intended as a fast, easy to administer and secure alternative to the widely-used Sendmail. ...

There are no programs to specifically defragment 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, Reiser4 will have a repacker that optimizes file fragmentation.^[6] It has been suggested that this article or section be merged with File system fragmentation. ...

fsck

The tree rebuild process of ReiserFS's fsck has attracted much criticism: If the file system becomes so badly corrupt that its internal tree is unusable, performing a tree rebuild operation may further corrupt existing files or introduce new entries with unexpected contents ^[7]. 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. The system utility fsck (for file system check or file system consistency check) is a tool for checking the consistency of a file system in the Unix system and clones thereof. ...

Nevertheless it is recommended not to store ReiserFS v3 images on a ReiserFS v3 partition (e.g. backups or disk images for emulators) without transforming them to a form that avoids misleading the file system, e.g., by compressing or encrypting. 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. In computer engineering, hard disk drive partitioning is the creation of logical divisions upon a hard disk that allows one to apply operating system-specific logical formatting. ... A disk image is a computer file containing the complete contents and structure of a data storage medium or device, such as a CD. The term has been generalized to cover any such file, whether taken from an actual physical storage device or not. ...

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.^[8] Network File System (NFS) is a network file system protocol originally developed by Sun Microsystems in 1984, allowing a user on a client computer to access files over a network as easily as if the network devices were attached to its local disks. ...

Early implementations of ReiserFS (prior to that in Linux 2.6.2) were also susceptible to out-of-order write hazards. For example, files being appended to during a crash gained a tail of garbage upon next mount.^{[citation needed]} But the current journaling implementation in ReiserFS is now on par with that of ext3's "ordered" journaling level. The ext3 or third extended filesystem is a journalled file system that is commonly used by the Linux operating system. ...

Design

ReiserFS stores file metadata ("stat items"), directory entries ("directory items"), inode block lists ("indirect items"), and tails of files ("direct items") in a single, combined B+ tree 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 bitmaps in fixed locations. In computing, a directory, catalog, or folder, is an entity in a file system which can contain a group of files and/or other directories. ... In computing, an inode is a data structure on a traditional Unix-style file system such as UFS. An inode stores basic information about a regular file, directory, or other file system object. ... A computer file is a collection of information that is stored in a computer system and can be identified by its full path name. ... A simple B+ tree example linking the keys 1-7 to data values d1-d7. ...

By contrast, ext2 and other Berkeley FFS-like file systems simply use a fixed formula for computing inode locations, hence limiting the number of files they may contain.^[9] Most such file systems also store directories as simple lists of entries, which makes directory lookups and updates linear time operations and degrades performance on very large directories. The single B+ tree design in ReiserFS avoids both of these problems due to better scalability properties. The ext2 or second extended file system is a file system for the Linux kernel. ... In computing, the Berkeley Fast File System (or FFS) is a file system used mostly by BSD-derivative Unix variants. ... In computational complexity, an algorithm is said to take linear time, or O(n) time, if the time it requires is proportional to the size of the input, which is usually denoted n. ... A simple B+ tree example linking the keys 1-7 to data values d1-d7. ...

See also

• Comparison of file systems
• Reiser4
• Namesys

The following tables compare general and technical information for a number of file systems. ... 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. ... Namesys is the company based in the United States and Russia owned and run by Hans Reiser. ...

Notes and references

1. ^ http://news.com.com/Novell+makes+file-storage+software+shift/2100-1016_3-6125509.html
2. ^ Hans Reiser, Reiser4 design, Problems with BLOBs. Retrieved 15. July 2006
3. ^ Daniel Robbins (2001), "Advanced file system implementor's guide". Retrieved 5. July 2006
4. ^ Matthias Andree (2001), LKML post on Postfix synchronity assumptions. Retrieved 15. July 2006
5. ^ http://archives.neohapsis.com/archives/postfix/2001-05/1749.html
6. ^ Hans Reiser, Reiser4 design, repacker. Retrieved 5. July 2006
7. ^ Theodore Ts'o LKML post. Retrieved 5. July 2006
8. ^ ReiserFS download page, see warning. Retrieved 5. July 2006
9. ^ Mingming Cao, Theodore Y. Ts'o, Badari Pulavarty, Suparna Bhattacharya (2005-07-26). "State of the Art: Where we are with the Ext3 file system". 2005 Linux Symposium, Ottawa, Canada: IBM Linux Technology Center. Retrieved on 2007-03-08. 

The Linux kernel mailing list (LKML) is the main electronic mailing list for Linux kernel development[1][2], where majority of the announcements, discussions, debates, and flame wars over the kernel take place[3]. Many other mailing lists exist to discuss the different subsystems and ports of the Linux kernel... Theodore Ted Tso (born 1968) is a software developer known for his contributions to the Linux kernel, in particular his contributions to file systems. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... July 26 is the 207th day (208th in leap years) of the year in the Gregorian calendar, with 158 days remaining. ... 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the CE era. ... March 8 is the 67th day of the year (68th in leap years) in the Gregorian calendar. ...

External links

• Namesys web site
• Theodore Ts'o critiques the ReiserFS block journaling implementation
• convertfs, a utility which performs in-place conversion between any two file systems with sparse file support
• An overview of the ReiserFS on-disk format
• Florian Buchholz's The structure of the Reiser file system, a very detailed description of the ReiserFS disk structures.
• Gentoo Forum Link - Discussion on ReiserFS fragmentation, including a script which for measuring fragmentation and defragmenting files.