UNIX Filesystems: Evolution, Design, and Implementation

The ext2 and ext3 Filesystems

The first filesystem that was developed as part of Linux was a Minix filesystem clone. At this time, the Minix filesystem stored its block addresses in 16-bit integers that restricted the size of the filesystem to 64MB. Also, directory entries were fixed in size and therefore filenames were limited to 14 characters. Minix filesystem support was replaced in 1992 by the ext filesystem, which supported filesystem sizes up to 2GB and filename sizes up to 255 characters. However, ext inodes did not have separate access, modification, and creation time stamps, and linked lists were used to manage free blocks and inodes resulting in fragmentation and less-than-ideal performance.

These inadequacies were addressed by both the Xia filesystem and the ext2 filesystem (which was modelled on the BSD Fast File System), both of which provided a number of enhancements, including a better on-disk layout for managing filesystem resources. The improvements resulting in ext2 far outweighed those of Xia, and in ext2 became the defacto standard on Linux.

The following sections first describe the ext2 filesystem, followed by a description of how the filesystem has evolved over time to produce the ext3 filesystem which supports journaling and therefore fast recovery.

Features of the ext2 Filesystem

Shown below are the main features supported by ext2:

4TB filesystems. This required changes within the VFS layer. Note that the maximum file and filesystem size are properties of ...