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Ext3 is a general-purpose filesystem with POSIX semantics. It was developed as part of the Linux Kernel and is the successor to Ext2. At the time of writing (December 2011) it was still the default filesystem for some GNU/Linux distributions, but it is in the process of being superseded by Ext4 and Btrfs.

With a block size of 4KB the maximum size of an Ext2 volume is 16TB and the maximum size of an individual file is 2TB. Filenames are limited to 255 bytes in length, with only two characters (forward slash and null) forbidden. It can efficiently handle large numbers of files per directory provided that the dir_index feature is enabled.

The main advantage of Ext3 over Ext2 is its support for journalling. Changes to the filesystem are written to a separate area of storage called a journal before they are committed, which greatly improves the ability of the filesystem to recover from failures that prevent it from being cleanly unmounted. However you should be aware that there are different modes in which the journal can operate (journal, ordered and writeback) and they do not give equal protection against data corruption in the event of a failure.


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Further reading