ext4

The ext4 journaling file system or fourth extended filesystem is a journaling file system for Linux, developed as the successor to ext3. It is the default file system for most Linux distributions. ext4 was initially a series of backward-compatible extensions to ext3, many of them originally developed by Cluster File Systems for the Lustre file system between 2003 and 2006, meant to extend storage limits and add other performance improvements. However, other Linux kernel developers opposed accepting extensions to ext3 for stability reasons, and proposed to fork the source code of ext3, rename it as ext4, and perform all the development there, without affecting the current ext3 users. This proposal was accepted, and on 28 June 2006, Theodore Ts'o, the ext3 maintainer, announced the new plan of development for ext4. A preliminary development version of ext4 was included in version 2.6.19 of the Linux kernel. On 11 October 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 25 December 2008. On 15 January 2010, Google announced that it would upgrade its storage infrastructure from ext2 to ext4. On 14 December 2010, Google also announced it would use ext4, instead of YAFFS, on Android 2.3. In 2008, the principal developer of the ext3 and ext4 file systems, Theodore Ts'o, stated that although ext4 has improved features, it is not a major advance, it uses old technology, and is a stop-gap. Ts'o believes that Btrfs is the better direction because 'it offers improvements in scalability, reliability, and ease of management.' Btrfs also has 'a number of the same design ideas that reiser3/4 had'. However, ext4 has continued to gain new features such as file encryption and metadata checksums. The ext4 file system does not honor the 'secure deletion' file attribute, which is supposed to cause overwriting of files upon deletion. A patch to implement secure deletion was proposed in 2011, but did not solve the problem of sensitive data ending up in the file system journal.