Ext3
| Developer(s) | Stephen Tweedie |
|---|---|
| Full name | Third extended file system |
| Introduced | November 2001 with Linux 2.4.15 |
| Partition identifier | 0x83 (MBR) EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 (GPT) |
| Structures | |
| Directory contents | Table, hashed B-tree with dir_index enabled |
| File allocation | bitmap (free space), table (metadata) |
| Bad blocks | Table |
| Limits | |
| Max. volume size | 4 TiB – 32 TiB |
| Max. file size | 16 GiB – 2 TiB |
| Max. number of files | Variable, allocated at creation time |
| Max. filename length | 255 bytes |
| Allowed characters in filenames | All bytes except NUL ('\0') and '/' |
| Features | |
| Dates recorded | modification (mtime), attribute modification (ctime), access (atime) |
| Date range | December 14, 1901 – January 18, 2038 |
| Date resolution | 1 s |
| Attributes | allow-undelete, append-only, h-tree (directory), immutable, journal, no-atime, no-dump, secure-delete, synchronous-write, top (directory) |
| File system permissions | Unix permissions, ACLs and arbitrary security attributes (Linux 2.6 and later) |
| Transparent compression | No |
| Transparent encryption | No (provided at the block device level) |
| Data deduplication | No |
| Other | |
| Supported operating systems | Linux, BSD, ReactOS,Windows (through an IFS) |
ext3, or third extended filesystem, is a journaled file system that is commonly used by the Linux kernel. It is the default file system for many popular Linux distributions. Stephen Tweedie first revealed that he was working on extending ext2 in Journaling the Linux ext2fs Filesystem in a 1998 paper, and later in a February 1999 kernel mailing list posting. The filesystem was merged with the mainline Linux kernel in November 2001 from 2.4.15 onward. Its main advantage over ext2 is journaling, which improves reliability and eliminates the need to check the file system after an unclean shutdown. Its successor is ext4.
The performance (speed) of ext3 is less attractive than competing Linux filesystems, such as ext4, JFS, ReiserFS, and XFS, but ext3 has a significant advantage in that it allows in-place upgrades from ext2 without having to backup and restore data. Benchmarks suggest that ext3 also uses less CPU power than ReiserFS and XFS. It is also considered safer than the other Linux file systems, due to its relative simplicity and wider testing base.
ext3 adds the following features to ext2:
Without these features, any ext3 file system is also a valid ext2 file system. This situation has allowed well-tested and mature file system maintenance utilities for maintaining and repairing ext2 file systems to also be used with ext3 without major changes. The ext2 and ext3 file systems share the same standard set of utilities, e2fsprogs, which includes an fsck tool. The close relationship also makes conversion between the two file systems (both forward to ext3 and backward to ext2) straightforward.
ext3 lacks "modern" filesystem features, such as dynamic inode allocation and extents. This situation might sometimes be a disadvantage, but for recoverability, it is a significant advantage. The file system metadata is all in fixed, well-known locations, and data structures have some redundancy. In significant data corruption, ext2 or ext3 may be recoverable, while a tree-based file system may not.
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