Editing Ext3 (section)

===Journaling levels===
There are three levels of [[Journaling file system|journaling]] available in the Linux implementation of ext3:

; Journal (lowest risk): Both metadata and file contents are written to the journal before being committed to the main file system. Because the journal is relatively continuous on disk, this can improve performance, if the journal has enough space. In other cases, performance gets worse, because the data must be written twice—once to the journal, and once to the main part of the filesystem.<ref name=devworks-part8 />

; Ordered (medium risk): Only metadata is journaled; file contents are not, but it's guaranteed that file contents are written to disk before associated metadata is marked as committed in the journal. This is the default on many Linux distributions. If there is a power outage or [[kernel panic]] while a file is being written or appended to, the journal will indicate that the new file or appended data has not been "committed", so it will be purged by the cleanup process. (Thus appends and new files have the same level of integrity protection as the "journaled" level.) However, files being ''overwritten'' can be corrupted because the original version of the file is not stored. Thus it's possible to end up with a file in an intermediate state between new and old, without enough information to restore either one or the other (the new data never made it to disk completely, and the old data is not stored anywhere). Even worse, the intermediate state might intersperse old and new data, because the order of the write is left up to the disk's hardware.<ref name=devworks-part8>{{Cite web |url=http://www.ibm.com/developerworks/library/l-fs8.html |title=Common threads: Advanced filesystem implementor's guide, Part 8 |work=IBM developerWorks |author=Daniel Robbins |author-link=Daniel Robbins (computer programmer) |date=2001-12-01 |archive-url=https://web.archive.org/web/20071013213924/http://www.ibm.com/developerworks/linux/library/l-fs8.html |archive-date=2007-10-13 }}</ref><ref>[http://evuraan.blogspot.com/2007/01/speeding-up-ext3-filesystems.html curious onloooker: Speeding up ext3 filesystems]. Evuraan.blogspot.com (2007-01-09). Retrieved on 2013-06-22.</ref>

; Writeback (highest risk): Only metadata is journaled; file contents are not. The contents might be written before or after the journal is updated. As a result, files modified right before a crash can become corrupted. For example, a file being appended to may be marked in the journal as being larger than it actually is, causing garbage at the end. Older versions of files could also appear unexpectedly after a journal recovery. The lack of synchronization between data and journal is faster in many cases. JFS uses this level of journaling, but ensures that any "garbage" due to unwritten data is zeroed out on reboot. XFS also uses this form of journaling.

In all three modes, the internal structure of file system is assured to be consistent even after a crash. In any case, only the data content of files or directories which were being modified when the system crashed will be affected; the rest will be intact after recovery.