The EXT3 or third extended filesystem is a journalled filesystem which is coming into increasing use among users of the GNU/Linux operating system. Although its performance and scalability is less attractive than many of its competitors such as ReiserFS and XFS it does have the significant advantage that users can upgrade from the popular EXT2 filesystem without having to backup and restore data.
The EXT3 filesystem adds a journal without which the filesystem is a valid EXT2 filesystem. A EXT3 filesystem can be mounted and used as an EXT2 filesystem. All of the file system maintenance utilities (like fsck) for maintaining and repairing the EXT2 filesystem can also be used with the EXT3 filesystem, which means EXT3 has a much more mature and well-tested set of maintenance utilities available than do its competitors.