Reiser4

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Reiser4
Developer	Namesys
Full name	Reiser4
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	8 TiB on x86
Max number of files
Max filename size	3976 bytes
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 timestamps^[1]
Date resolution
Forks	Extended attributes
Attributes
File system permissions	Unix permissions, ACLs and arbitrary security attributes
Transparent compression	Version 4.1 (beta)
Transparent encryption	Version 4.1 (beta)
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 2007, Reiser4 has not yet been merged into the mainline Linux kernel and consequently is still not supported on many Linux distributions; however, its predecessor ReiserFS v3 has been much more widely adopted. Reiser4 is also available from Andrew Morton's -mm kernel sources. Linux kernel developers claim that Reiser4 breaks Linux coding standards,^[2] but Hans Reiser suggests political reasons.^{[citation needed]}

1 Features
2 Performance
3 References
4 See also
5 External links

[edit] Features

Some of the goals of the Reiser4 file system are:

More efficient journaling through wandering logs
More efficient support of small files, in terms of disk space and speed through tail packing
Faster handling of directories with large numbers 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

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; sooner if someone pays them to do so.^[3]

[edit] Performance

Reiser4 uses B*-trees in conjunction with the dancing tree balancing approach, in which underpopulated nodes will not 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 1 KiB. Namesys's benchmarks suggest it is typically twice the performance of ext3 for general-purpose filesystem usage patterns.^[4] Other benchmarks show results of Reiser4 being slower on many operations.^[5]

[edit] References

^ Documentation/filesystems/reiser4.txt from a reiser4-patched kernel source, "By default file in reiser4 have 64 bit timestamps."
^ Linux: Why Reiser4 Is Not in the Kernel. Kerneltrap (September 19, 2005).
^ Reiser, Hans (2004-09-16). Re: Benchmark : ext3 vs reiser4 and effects of fragmentation.. Namesys, ReiserFS mailing list. Retrieved on 2006-10-13.
^ Hans Reiser (November 20, 2003). Benchmarks Of ReiserFS Version 4. Namesys. Retrieved on 2006-11-28.
^ Justin Piszcz (januari 2006). Benchmarking Filesystems Part II. Retrieved on 2006-04-23.