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| Developer(s) | Edward Shishkin and others[1] |
|---|---|
| Full name | Reiser4 |
| Introduced | 2004; 22 years ago (2004) withLinux |
| Partition IDs | Apple_UNIX_SVR2 (Apple Partition Map)
Basic data partition (GPT) |
| Structures | |
| Directory contents | DancingB*-tree |
| Limits | |
| Max file size | 8TiB on x86 |
| Max filename length | 3976 bytes |
| Allowed filename characters | All bytes except NUL and '/' |
| Features | |
| Dates recorded | modification (mtime), metadata change (ctime), access (atime) |
| Date range | 64-bit timestamps[2] |
| Forks | No |
| File system permissions | Unix permissions |
| Transparent compression | Yes |
| Transparent encryption | No |
| Data deduplication | No |
| Other | |
| Supported operating systems | Linux |
| Website | reiser4.wiki.kernel.org |
| Repository | github.com/edward6/reiser4 |
Reiser4 is acomputerfile system, successor to theReiserFS file system, developed from scratch byNamesys and sponsored byDARPA as well asLinspire. Reiser4 was named after its former lead developerHans Reiser. As of 2021[update], the Reiser4 patch set is still being maintained,[3][4] but according toPhoronix, it is unlikely to be merged into mainline Linux without corporate backing.[5]
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 aVFS API for them.
At present Reiser4 lacks a few standard file system features, such as an online repacker (similar to thedefragmentation 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.[11]
Reiser4 usesB*-trees in conjunction with thedancing 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.
As of 2004[update], synthetic benchmarks performed by Namesys in 2003 show that Reiser4 is 10 to 15 times faster than its most serious competitorext3 working on files smaller than 1KiB. Namesys's benchmarks suggest it is typically twice the performance of ext3 for general-purpose filesystem usage patterns.[12] Other benchmarks from 2006 show results of Reiser4 being slower on many operations.[13] Benchmarks conducted in 2013 with Linux Kernel version 3.10 show that Reiser4 is considerably faster in various tests compared to in-kernel filesystemsext4,btrfs andXFS.[14]
Reiser4 has patches for Linux 2.6, 3.x, 4.x and 5.x.,[15][3] but as of 2019[update], Reiser4 has not been merged into the mainlineLinux kernel[3] and consequently is still not supported on manyLinux distributions; however, its predecessor ReiserFS v3 has been widely adopted. Reiser4 is also available fromAndrew 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,[16] butHans Reiser suggested the decision was made for political reasons.[17]The latest released Reiser4 kernel patches and tools can be downloaded from Reiser4 project page at sourceforge.net.[4]
Hans Reiser wasconvicted of murder 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;[18] as of March 26, 2008, it had not been sold, although the website was unavailable. During aCNET interview in January 2008, Edward Shishkin, an employee and programmer working for Namesys, said: "Commercial activity of Namesys has stopped." Shishkin and others continued the development of Reiser4,[19] making source code available from Shishkin's web site,[20] later relocated tokernel.org.[21] Since 2008, Namesys employees have received 100% of their sponsored funding fromDARPA.[22][23][24]
In 2010,Phoronix wrote that Edward Shishkin was exploring options to get Reiser4 merged into Linux kernel mainline.[25] As of 2019[update], the file system is still being updated for new kernel releases, but has not been submitted for merging.[3] In 2015,Michael Larabel mentioned it is unlikely to happen without corporate backing,[26] and then he suggested in April 2019 that the main obstacle could be the renaming of Reiser4 so as to avoid any references to Reiser.[3]
Shishkin announced a Reiser5 filesystem on December 31, 2019.[27]
