Reiser4
Encyclopedia : R : RE : REI : Reiser4
| Reiser4 | |
|---|---|
| Developer | Namesys |
| Full name | ReiserFS 4 |
| Introduced | 2004 (Linux) |
| Partition identifier | Apple_UNIX_SVR2 (Apple Partition Map) 0x83 (MBR) EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 (GPT) |
| Structures | |
| Directory contents | Dancing B*-tree |
| File allocation | |
| Bad blocks | |
| Limits | |
| Max file size | 8TiB on x86 |
| Max number of files | |
| Max filename size | |
| Max volume size | |
| Allowed characters in filenames | All bytes except NUL and '/' |
| Features | |
| Dates recorded | modification (mtime), metadata change (ctime), access (atime) |
| Date range | 64-bit timestampsDocumentation/filesystems/reiser4.txt from a reiser4-patched kernel source, "By default file in reiser4 have 64 bit timestamps." |
| Forks | Extended attributes |
| Attributes | |
| File system permissions | Unix permissions, ACLs and arbitrary security attributes |
| Transparent compression | compile-time plugin |
| Transparent encryption | compile-time plugin |
| Supported operating systems | Linux |
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.
As of July 15, 2006, Reiser4 still has not been merged into the mainline Linux kernel due to not adhering to Linux's coding standards and consequently is not supported on many Linux distributions except Linspire; however, its predecessor ReiserFS v3 has been much more widely adopted. Reiser4 is also available from Andew Morton's -mm kernel sources. Namesys has made inclusion into the mainline Linux kernel its first priority.
Features
- Efficient journaling through wandering logs
- Efficient support of small files, in terms of disk space and speed
- Fast handling of very large directories with hundreds of millions of files
- Flexible plugin infrastructure (through which special metadata types, encryption and compression will be supported)
- Dynamically optimized disk-layout through allocate-on-flush (also called delayed allocation in XFS)
- Transaction support
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; sooner if someone pays them to do so.
Performance
Reiser4 uses B*-trees in conjuction with the dancing tree balancing approach, in which underpopulated nodes won't get 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, synthetic benchmarks performed by Namesys show that Reiser4 is 10 to 15 times faster than its most serious competitor ext3 working on files smaller than 1KiB. Namesys' benchmarks suggest it is typically twice the performance of ext3 for general-purpose filesystem usage patterns.
Notes and references
See also
- List of file systems
- Comparison of file systems
External links
- [Reiser4 homepage]
- [Reiser4 Future Vision]
- [Introduction to Reiser4 on kuro5hin]
- [Getting started with Reiser4] from Namesys.com
- [Programmer's Guide to Reiser4]
- [Hans Reiser: The Reiser4 Filesystem]
- [Why Resier 4 is not in mainline kernel FAQ]
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