The ext4 or fourth extended filesystem is a new linux based journaling file system developed as the successor to ext3.The result of three years of Ext4 development has been significant advances from Ext3 which increase the volume limit to 1024 PB. This should be sufficient for many years to come. Extents, long implemented in other file systems such as XFS, should improve the efficiency of managing large files. There are also a whole range of under-the-bonnet changes intended to improve Ext4 performance compared to Ext3.

In 2006, the Linux developer, Theodore Ts’o, who was, at the time, the ext3 maintainer, began work on ext4. Unlike ext3, which just added some features to ext2 while keeping the on-line format and approach of ext2, ext4 is a fork of ext3 that is a deep code change affecting the data structures used in ext4 to make it a better file system - faster, more reliable, more features, better code, etc. Ext4 brought ext3 into the world of 64-bits allowing individual files of 16TB (assuming 4KB blocks), as well file systems of 1 Exabyte (EB) by using 48-bit data structures. One EB is the same as 1,048,576 Terabytes (TB).

A preliminary development snapshot of ext4 was included in version 2.6.19 of the Linux kernel. On Oct 11, 2008, the patches that mark ext4 as stable code were merged in the Linux 2.6.28 source code repositories,denoting the end of the development phase and recommending ext4 adoption. Kernel 2.6.28, containing the ext4 filesystem, was finally released on December 25, 2008.

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