Ext4
| Developer(s) | Mingming Cao, Andreas Dilger, Alex Zhuravlev (Tomas), Dave Kleikamp, Theodore Ts'o, Eric Sandeen, Sam Naghshineh, others |
|---|---|
| Full name | Fourth extended file system |
| Introduced | 10 October 2006 with Linux 2.6.19 |
| Preceded by | ext3 |
| Partition IDs | 0x83: MBR / EBR. EBD0A0A2-B9E5-4433-87C0-68B6B72699C7: GPT Windows BDP.[1] |
| Structures | |
| Directory contents | Linked list, hashed B-tree |
| File allocation | Extents / Bitmap |
| Bad blocks | Table |
| Limits | |
| Max volume size | 1 EiB |
| Max file size | 16–256 TiB (for 4–64 KiB block size) |
| Max no. of files | 4 billion (specified at filesystem creation time) |
| Max filename length | 255 bytes (fewer for multibyte character encodings such as Unicode) |
| Allowed filename characters | All characters and character sequences permitted, except for NULL ('\0'), '/', and the special file names "." and ".." which are reserved for indicating (respectively) current and parent directories. |
| Features | |
| Dates recorded | modification (mtime), data or attribute modification (ctime), access (atime), delete (dtime), create (crtime) |
| Date range | 14 December 1901 – 10 May 2446[3] |
| Date resolution | Nanosecond |
| Forks | No |
| Attributes | acl, bh, bsddf, commit=nrsec, data=journal, data=ordered, data=writeback, delalloc, extents, journal_dev, mballoc, minixdf, noacl, nobh, nodelalloc, noextents, nomballoc, nombcache, nouser_xattr, oldalloc, orlov, user_xattr |
| File system permissions | Unix permissions, POSIX ACLs |
| Transparent compression | No |
| Transparent encryption | Yes |
| Data deduplication | No |
| Other | |
| Supported operating systems | |
ext4 (fourth extended filesystem) is a journaling file system for Linux, developed as the successor to ext3.
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.[4] However, other Linux kernel developers opposed accepting extensions to ext3 for stability reasons,[5] and proposed to fork the source code of ext3, rename it as ext4, and perform all the development there, without affecting existing 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.[6]
A preliminary development version of ext4 was included in version 2.6.19[7] 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,[8] 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.[9] On 15 January 2010, Google announced that it would upgrade its storage infrastructure from ext2 to ext4.[10]
ext4 (fourth extended filesystem) is a journaling file system for Linux. ext4 is the default filesystem for many distributions, such as Debian and Ubuntu. It is made to use as much of the space available as possible. The file system is also used on FreeBSD and other UNIX based operating systems.
References
- ↑ 1.0 1.1 Previously, Linux used the same GUID for the data partitions as Windows (Basic data partition: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7). Linux never had a separate unique partition type GUID defined for its data partitions. This created problems when dual-booting Linux and Windows in UEFI-GPT setup. The new GUID (Linux filesystem data: 0FC63DAF-8483-4772-8E79-3D69D8477DE4) was defined jointly by GPT fdisk and GNU Parted developers. It is identified as type code 0x8300 in GPT fdisk. (See definitions in gdisk's parttypes.cc)
- ↑ "DiscoverablePartitionsSpec". freedesktop.org. Retrieved 7 April 2018.
- ↑ "ext4: Fix handling of extended tv_sec". Linux-stable kernel tree. Retrieved 2017-02-14.
- ↑ Mathur, Avantika; Cao, MingMing; Bhattacharya, Suparna; Dilger, Andreas; Zhuravlev (Tomas), Alex; Vivier, Laurent (2007). "The new ext4 filesystem: current status and future plans" (PDF). Proceedings of the Linux Symposium. Ottawa, ON, CA: Red Hat. Archived from the original (PDF) on 2010-07-06. Retrieved 2008-01-15.
- ↑ Torvalds, Linus (2006-06-09). "extents and 48bit ext3". Linux kernel mailing list.
- ↑ Ts'o, Theodore (2006-06-28). "Proposal and plan for ext2/3 future development work". Linux kernel mailing list.
- ↑ Leemhuis, Thorsten (2008-12-23). "Higher and further: The innovations of Linux 2.6.28 (page 2)". Heise Online. Archived from the original on 2009-01-03. Retrieved 2010-01-09.
- ↑ "ext4: Rename ext4dev to ext4". Linus' kernel tree. Archived from the original on 29 May 2012. Retrieved 2008-10-20.
- ↑ Leemhuis, Thorsten (2008-12-23). "Higher and further: The innovations of Linux 2.6.28". Heise Online.
- ↑ Paul, Ryan (2010-01-15). "Google upgrading to Ext4, hires former Linux Foundation CTO". Ars Technica.
Other websites
- ext4 documentation in Linux kernel source
- Theodore Ts'o's discussion on ext4, 29 June 2006
- "ext4 online defragmentation" Archived 30 December 2019 at the Wayback Machine (materials from Ottawa Linux Symposium 2007)
- "The new ext4 filesystem: current status and future plans" (materials from Ottawa Linux Symposium 2007)
- Kernel Log: Ext4 completes development phase as interim step to btrfs, 17 October 2008
- "Ext4 block and inode allocator improvements" Archived 31 March 2010 at the Wayback Machine (materials from Ottawa Linux Symposium 2008)
- "Ext4: The Next Generation of Ext2/3 Filesystem"
- Ext4 (and Ext2/Ext3) Wiki
- Ext4 wiki at kernelnewbies.org
- Native Windows port of Ext4 and other FS in CROSSMETA
- Ext2read A windows application to read/copy ext2/ext3/ext4 files with extent and LVM2 support.
- Ext2Fsd Open source ext2/ext3/ext4 read/write file system driver for Windows. ext4 is supported from version 0.50 onwards
- Ext4fuse Open source read-only ext4 driver for FUSE. (Supports Mac OS X 10.5 and later, using MacFuse)
- oracle post Understanding ext4 disk layout