ReiserFS
also: Reiser3, Reiser version 3
ReiserFS is a journaling filesystem for Linux that was popular in the early 2000s, known for efficient handling of small files and dynamic inode allocation.
ReiserFS was developed by Hans Reiser and introduced in 2001 as an alternative to ext2/ext3. It featured a B+ tree-based structure that allowed it to pack small files and metadata efficiently into disk blocks, reducing wasted space and improving performance for workloads with many small files.
The filesystem included journaling capabilities to protect against data loss during unexpected shutdowns. ReiserFS version 3 was widely used on servers and desktop systems, particularly on SuSE Linux distributions, though it was less common than ext3.
ReiserFS has largely been superseded by ext4, Btrfs, and XFS. It is now considered legacy, with minimal maintenance and most modern distributions removing support. Its creator's imprisonment in 2006 also contributed to the decline in development and adoption.