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A Brief History Of EXT2, EXT3, And EXT4
By: Bryan Young
Expert Author
2011-12-13
In 1992, the first extended file system (EXT) was created especially for Linux, and it has not been immune to changes over the last two decades. The first change to ext happened the following year with the creation of the second extended filesystem (EXT2). Another filesystem (xiafs) was created in parallel with EXT2, but is no longer used due to EXT2's flexibility and longevity.
EXT2 expanded on EXT in numerous ways. Developed by Rémy Card, it expanded the maximum filesystem size from 2 gigabytes to 32 terabytes (although on Linux kernel 2.4 and below, the maximum partition size is 2 terabytes regardless of filesystem). On flash drives and USB drives, EXT2 is the preferred filesystem in order to avoid the overhead of journaling.
EXT3 was developed in 2001 in order to expand upon EXT2 and is the first major Linux filesystem to enable journaling. Journaling entails writing all filesystem changes to a temporary location called a journal before writing the changes to the filesystem for real. This allows faster recovery from disaster scenarios and also a decreased chance of file corruption. An EXT2 system can be converted to EXT3 directly without having to backup and restore the information stored.
EXT4 is a fork of the EXT3 filesystem, started in 2006 and added to the Linux kernel in 2008. It was begun as a series of additions to EXT3, but became a fork to prevent creating instability problems for current EXT3 users. I would almost call it EXT3+ for this reason. The main improvements introduced in EXT4 are journal checksums and delayed file space allocation. By using checksums of the journal, EXT4 can improve write performance by skipping the traditional checks for disk I/O. Delayed file space allocation basically means that the filesystem waits until right before a file is to be written from the journal to the filesystem to allocate space for that file, which allows better decision making to take place. EXT4 is also fully backwards compatible with EXT2 and EXT3, so that both these filesystems can be mounted as EXT4 to take advantage of the extra features without needing to be reformatted.
About the Author:
Bryan Young is a staff writer for WebProNews.
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