ext2

Ext2, short for the second extended filesystem, is a legacy Linux filesystem introduced in the early 1990s as an improvement over the original ext format. It is a non-journaling filesystem that uses inodes, block groups, and bitmap structures to manage data and free space. Ext2 was designed for reliability and speed across a range of storage devices and workloads.

Key design features include support for relatively large volumes, flexible block sizing (commonly 1 KiB, 2 KiB, or 4 KiB blocks), and straightforward on-disk structures. Because ext2 does not maintain a journal of metadata changes, it can offer fast write performance in certain scenarios. However, its lack of journaling means that it is more susceptible to corruption after crashes or power failures, compared with journaling filesystems.

Historically, ext2 became widely adopted as the default filesystem for many Linux distributions during the 1990s and early 2000s. It laid a stable foundation for later extensions, notably ext3, which added metadata journaling, and ext4, which introduced further enhancements such as improved scalability and new on-disk structures. Ext2 remains supported in the Linux kernel and is still available via the e2fsprogs utilities, including tools for creation and maintenance.

Limitations and considerations include the absence of built-in journaling, which affects crash recovery guarantees. It also lacks some advanced features found in newer filesystems, such as extents and online resizing in the original form. Despite these drawbacks, ext2 is still used in certain environments, including embedded systems or scenarios where a simple, fast non-journaling filesystem is desired. It can be upgraded to ext3 by adding a journal and remounting, after which typical journaling benefits apply, and then further migrated to ext4 for additional improvements.