Ext2 - History

History

The early development of the Linux kernel was made as a cross-development under the Minix operating system. Naturally, it was obvious that the MINIX file system would be used as Linux's first file system. The Minix file system was mostly free of bugs, but used 16-bit offsets internally and thus had a maximum size limit of only 64 megabytes. There was also a filename length limit of 14 characters. Because of these limitations, work began on a replacement native file system for Linux.

To ease the addition of new file systems and provide a generic file API, VFS, a virtual file system layer, was added to the Linux kernel. The extended file system (ext), was released in April 1992 as the first file system using the VFS API and was included in Linux version 0.96c. The ext file system solved the two major problems in the Minix file system (maximum partition size and filename length limitation to 14 characters), and allowed 2 gigabytes of data and filenames of up to 255 characters. But it still had problems: there was no support of separate timestamps for file access, inode modification, and data modification.

As a solution for these problems, two new filesystems were developed in January 1993: xiafs and the second extended file system (ext2), which was an overhaul of the extended file system incorporating many ideas from the Berkeley Fast File System. ext2 was also designed with extensibility in mind, with space left in many of its on-disk data structures for use by future versions.

Since then, ext2 has been a testbed for many of the new extensions to the VFS API. Features such as POSIX ACLs and extended attributes were generally implemented first on ext2 because it was relatively simple to extend and its internals were well-understood.

On Linux kernels prior to 2.6.17, restrictions in the block driver mean that ext2 filesystems have a maximum file size of 2TB.

ext2 is still recommended over journaling file systems on bootable USB flash drives and other solid-state drives. ext2 performs fewer writes than ext3, since it does not need to write to the journal. As the major aging factor of a flash chip is the number of erase cycles, and as those happen frequently on writes, having fewer writes increases the life span of the solid-state device. Another good practice for filesystems on flash devices is the use of the noatime mount option, for the same reason.