Ext3
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- The title of this article is incorrect because of technical limitations. The correct title is ext3.
The ext3 or third extended filesystem is a journalled file system which is coming into increasing use among users of the Linux operating system. It is the default file system for the Red Hat, Fedora and Debian Linux distributions.
Although its performance and scalability is less attractive than many of its competitors such as ReiserFS and XFS it does have the significant advantage in that it allows in-place upgrades from the popular ext2 file system without having to backup and restore data.
The ext3 file system adds, over its predecessor:
Without these, any ext3 file system is also valid ext2 file system. This has allowed well-tested and mature file system maintenance utilities (like fsck) for maintaining and repairing ext2 file systems to also be used with ext3 without major changes. It also makes conversion between the two file systems (both forward to ext3 and backward to ext2) straightforward.
There are three levels of journalling available in the Linux implementation of ext3:
- Journal, where both metadata and file contents are written to the journal before being committed to the main filesystem. This improves reliability at a performance penalty because all data has to be written twice.
- Writeback, where metadata is journalled but file contents are not. This is faster, but introduces the hazard of out-of-order writes where, for example, files being appended to during a crash may gain a tail of garbage on the next mount.
- Ordered, as with "writeback", but forces file contents to be written after its associated metadata is. This is thought to be an acceptable compromise between reliability and performance, and hence is the default.
Online resizing has been implemented in ext3, but this functionality has yet to be merged into the mainline Linux kernel and the standard ext2/ext3 file system utilities.
Unlike ext2, ext3 zeroes out the block pointers in the inodes of deleted files. This makes it very hard to recover deleted files.
Support for transparent compression (available as an unofficial patch for ext2) is not available in ext3.
See also
External link
- Linux ext3 FAQ (http://batleth.sapienti-sat.org/projects/FAQs/ext3-faq.html)de:Ext3