Reiser4
| Developer(s) | Namesys |
|---|---|
| Full name | Reiser4 |
| Introduced | 2004 with Linux |
| Partition identifier |
Apple_UNIX_SVR2 (Apple Partition Map) |
| Structures | |
| Directory contents | Dancing B*-tree |
| Limits | |
| Max. file size | 8 TiB on x86 |
| Max. filename length | 3976 bytes |
| Allowed characters in filenames | All bytes except NULL and '/' |
| Features | |
| Dates recorded | modification (mtime), metadata change (ctime), access (atime) |
| Date range | 64-bit timestamps |
| Forks | No |
| File system permissions | Unix permissions |
| Transparent compression | Yes |
| Transparent encryption | No |
| Data deduplication | No |
| Other | |
| Supported operating systems | Linux |
Apple_UNIX_SVR2 (Apple Partition Map)
0x83 (MBR)
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. As of 2016, the Reiser4 patch set is still being maintained, but according to Phoronix, it's unlikely to be merged into mainline Linux without corporate backing.
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 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, or sooner if someone pays them to do so.
Reiser4 uses B*-trees in conjunction with the dancing 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 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. Other benchmarks from 2006 show results of Reiser4 being slower on many operations. Benchmarks conducted in 2013 with Linux Kernel version 3.10 show that Reiser4 is considerably faster in various tests compared to in-kernel filesystems EXT4, btrfs and XFS.
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