What are reiserfs?

ReiserFS

ReiserFS is a general-purpose, journaled computer file system designed and implemented by a team at Namesys led by Hans Reiser. ReiserFS is currently supported on Linux (without quota support). 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 Elive, Xandros, Linspire, GoboLinux, and Yoper 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 for future releases.

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Some articles on reiserfs:

Comparison Of Boot Loaders - Features
... FAT16, FAT32, MINIX fs, Linux ext2fs, ReiserFS, JFS, XFS, VSTa fs FreeBSD, NetBSD, OpenBSD, GNU/Linux ELF TFTP gzip GRUB 2 Yes Yes i386(PC, coreboot, OLPC, Mac), PowerPC(Mac, Pegasos II), Sun UltraSPARC(S ... FAT, VFAT, ext2, ext3, ext4, jffs2, cramfs, reiserfs, yaffs2, ubifs, nfs 4_4bsd, Artos, Dell, Esix, FreeBSD, Irix, Linux, LynxOS, NCR, NetBSD, OpenBSD, pSOS, QNX, RTEMS, SCO ... kexec-loader No No i386 most supported by Linux Kernel (ext2, ext3, ext4, reiserfs, xfs, jfs, etc..) Linux/multiboot ? No networking gzip (for kernel modules) Kernel/multiboo ...
Comparison Of Linux Distributions - Technical
... the default file system, but many Linux distributions support some or all of ext2, ext3, ext4, ReiserFS, Reiser4, JFS, XFS, GFS2, OCFS2, and NILFS ... Xfce EasyPeasy ext3 GNOME, Ubuntu Netbook Edition Elive SquashFS, ReiserFS Enlightenment EnGarde Secure Linux ext3 none Fedora ext4 GNOME Finnix SquashFS none Foresight Linux ext3 GNOME ... ext3 KDE Plasma Workspaces Linspire ReiserFS K Desktop Environment 3 Linux Mint ext4 MATE, Cinnamon Lunar Linux none none Mageia ext4 KDE Plasma Workspaces, GNOME Mandriva Linux ext4 KDE Plasma Workspaces MEPIS ...
ReiserFS - 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 ... The single B+ tree design in ReiserFS avoids both of these problems due to better scalability properties ...
Hans Reiser - Namesys and ReiserFS
... Main articles ReiserFS and Reiser4 Reiser and his company Namesys developed the journaled computer file systems ReiserFS and Reiser4 ... ReiserFS has been available in the Linux operating system since version 2.4.1 and has at times been the default filesystem on several Linux distributions including, until 2006, Novell's SUSE Linux Enterprise ...