ext3, or third extended filesystem, is a journaled file system that is commonly used by the Linux kernel. It used to be the default file system for many popular Linux distributions. Stephen Tweedie first revealed that he was working on extending ext2 in Journaling the Linux ext2fs Filesystem in a 1998 paper, and later in a February 1999 kernel mailing list posting. The filesystem was merged with the mainline Linux kernel in November 2001 from 2.4.15 onward. Its main advantage over ext2 is journaling, which improves reliability and eliminates the need to check the file system after an unclean shutdown. Its successor is ext4. Advantages The performance (speed) of ext3 is less attractive than competing Linux filesystems, such as ext4, JFS, ReiserFS, and XFS, but ext3 has a significant advantage in that it allows in-place upgrades from ext2 without having to back up and restore data. Benchmarks suggest that ext3 also uses less CPU power than ReiserFS and XFS. It is also considered safer than the other Linux file systems, due to its relative simplicity and wider testing base. ext3 adds the following features to ext2: A journal Online file system growth HTree indexing for larger directories Without these features, any ext3 file system is also a valid ext2 file system. This situation has allowed well-tested and mature file system maintenance utilities for maintaining and repairing ext2 file systems to also be used with ext3 without major changes. The ext2 and ext3 file systems share the same standard set of utilities, e2fsprogs, which includes an fsck tool. The close relationship also makes conversion between the two file systems (both forward to ext3 and backward to ext2) straightforward. ext3 lacks "modern" filesystem features, such as dynamic inode allocation and extents. This situation might sometimes be a disadvantage, but for recoverability, it is a significant advantage. The file system metadata is all in fixed, well-known locations, and data structures have some redundancy. In significant data corruption, ext2 or ext3 may be recoverable, while a tree-based file system may not. Size limits The maximum number of blocks for ext3 is 232. The size of a block can vary, affecting the maximum number of files and the maximum size of the file system: Journaling levels There are three levels of journaling available in the Linux implementation of ext3: Journal (lowest risk) Both metadata and file contents are written to the journal before being committed