ReiserFS is a general-purpose, journaling file system initially designed and implemented by a team at Namesys led by Hans Reiser and licensed under GPLv2.
Namesys considered ReiserFS stable and feature-complete and ceased development on it to concentrate on its successor, Reiser4, though it continued to release security updates and critical bug fixes.
Due to technical issues inherent to the file system and lack of maintenance, Linux community had been discussing removal of ReiserFS from mainline since at least early 2022.
Compared with ext2 and ext3 in version 2.4 of the Linux kernel, when dealing with files under 4 KiB and with tail packing enabled, ReiserFS may be faster.
[15][16] Jeff Mahoney of SUSE wrote a post on 14 September 2006 proposing to move from ReiserFS to ext3 for the default installation file system.
[12] The reasons he mentioned included scalability, "performance problems with extended attributes and ACLs", "a small and shrinking development community", and that "Reiser4 is not an incremental update and requires a reformat, which is unreasonable for most people.
[18][failed verification] Mahoney wrote he "was concerned that people would make a connection where none existed" and that "the timing is entirely coincidental and the motivation is unrelated.
Predictably, the process is destructive and may further corrupt existing files or introduce new entries with unexpected contents, which has been criticized as a less than optimal method.
Reformatting an existing ReiserFS v3 partition can also leave behind data that could confuse the rebuild operation and make files from the old system reappear.
ReiserFS in versions of the Linux kernel before 2.4.16 were considered unstable by Namesys and not recommended for production use, especially in conjunction with NFS.