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-
-Ext3 Filesystem
-===============
-
-Ext3 was originally released in September 1999. Written by Stephen Tweedie
-for the 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger,
-Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.
-
-Ext3 is the ext2 filesystem enhanced with journalling capabilities.
-
-Options
-=======
-
-When mounting an ext3 filesystem, the following option are accepted:
-(*) == default
-
-ro Mount filesystem read only. Note that ext3 will replay
- the journal (and thus write to the partition) even when
- mounted "read only". Mount options "ro,noload" can be
- used to prevent writes to the filesystem.
-
-journal=update Update the ext3 file system's journal to the current
- format.
-
-journal=inum When a journal already exists, this option is ignored.
- Otherwise, it specifies the number of the inode which
- will represent the ext3 file system's journal file.
-
-journal_dev=devnum When the external journal device's major/minor numbers
- have changed, this option allows the user to specify
- the new journal location. The journal device is
- identified through its new major/minor numbers encoded
- in devnum.
-
-norecovery Don't load the journal on mounting. Note that this forces
-noload mount of inconsistent filesystem, which can lead to
- various problems.
-
-data=journal All data are committed into the journal prior to being
- written into the main file system.
-
-data=ordered (*) All data are forced directly out to the main file
- system prior to its metadata being committed to the
- journal.
-
-data=writeback Data ordering is not preserved, data may be written
- into the main file system after its metadata has been
- committed to the journal.
-
-commit=nrsec (*) Ext3 can be told to sync all its data and metadata
- every 'nrsec' seconds. The default value is 5 seconds.
- This means that if you lose your power, you will lose
- as much as the latest 5 seconds of work (your
- filesystem will not be damaged though, thanks to the
- journaling). This default value (or any low value)
- will hurt performance, but it's good for data-safety.
- Setting it to 0 will have the same effect as leaving
- it at the default (5 seconds).
- Setting it to very large values will improve
- performance.
-
-barrier=<0|1(*)> This enables/disables the use of write barriers in
-barrier (*) the jbd code. barrier=0 disables, barrier=1 enables.
-nobarrier This also requires an IO stack which can support
- barriers, and if jbd gets an error on a barrier
- write, it will disable again with a warning.
- Write barriers enforce proper on-disk ordering
- of journal commits, making volatile disk write caches
- safe to use, at some performance penalty. If
- your disks are battery-backed in one way or another,
- disabling barriers may safely improve performance.
- The mount options "barrier" and "nobarrier" can
- also be used to enable or disable barriers, for
- consistency with other ext3 mount options.
-
-user_xattr Enables Extended User Attributes. Additionally, you
- need to have extended attribute support enabled in the
- kernel configuration (CONFIG_EXT3_FS_XATTR). See the
- attr(5) manual page and http://acl.bestbits.at/ to
- learn more about extended attributes.
-
-nouser_xattr Disables Extended User Attributes.
-
-acl Enables POSIX Access Control Lists support.
- Additionally, you need to have ACL support enabled in
- the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL).
- See the acl(5) manual page and http://acl.bestbits.at/
- for more information.
-
-noacl This option disables POSIX Access Control List
- support.
-
-reservation
-
-noreservation
-
-bsddf (*) Make 'df' act like BSD.
-minixdf Make 'df' act like Minix.
-
-check=none Don't do extra checking of bitmaps on mount.
-nocheck
-
-debug Extra debugging information is sent to syslog.
-
-errors=remount-ro Remount the filesystem read-only on an error.
-errors=continue Keep going on a filesystem error.
-errors=panic Panic and halt the machine if an error occurs.
- (These mount options override the errors behavior
- specified in the superblock, which can be
- configured using tune2fs.)
-
-data_err=ignore(*) Just print an error message if an error occurs
- in a file data buffer in ordered mode.
-data_err=abort Abort the journal if an error occurs in a file
- data buffer in ordered mode.
-
-grpid Give objects the same group ID as their creator.
-bsdgroups
-
-nogrpid (*) New objects have the group ID of their creator.
-sysvgroups
-
-resgid=n The group ID which may use the reserved blocks.
-
-resuid=n The user ID which may use the reserved blocks.
-
-sb=n Use alternate superblock at this location.
-
-quota These options are ignored by the filesystem. They
-noquota are used only by quota tools to recognize volumes
-grpquota where quota should be turned on. See documentation
-usrquota in the quota-tools package for more details
- (http://sourceforge.net/projects/linuxquota).
-
-jqfmt=<quota type> These options tell filesystem details about quota
-usrjquota=<file> so that quota information can be properly updated
-grpjquota=<file> during journal replay. They replace the above
- quota options. See documentation in the quota-tools
- package for more details
- (http://sourceforge.net/projects/linuxquota).
-
-Specification
-=============
-Ext3 shares all disk implementation with the ext2 filesystem, and adds
-transactions capabilities to ext2. Journaling is done by the Journaling Block
-Device layer.
-
-Journaling Block Device layer
------------------------------
-The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed
-to add journaling capabilities to a block device. The ext3 filesystem code
-will inform the JBD of modifications it is performing (called a transaction).
-The journal supports the transactions start and stop, and in case of a crash,
-the journal can replay the transactions to quickly put the partition back into
-a consistent state.
-
-Handles represent a single atomic update to a filesystem. JBD can handle an
-external journal on a block device.
-
-Data Mode
----------
-There are 3 different data modes:
-
-* writeback mode
-In data=writeback mode, ext3 does not journal data at all. This mode provides
-a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
-mode - metadata journaling. A crash+recovery can cause incorrect data to
-appear in files which were written shortly before the crash. This mode will
-typically provide the best ext3 performance.
-
-* ordered mode
-In data=ordered mode, ext3 only officially journals metadata, but it logically
-groups metadata and data blocks into a single unit called a transaction. When
-it's time to write the new metadata out to disk, the associated data blocks
-are written first. In general, this mode performs slightly slower than
-writeback but significantly faster than journal mode.
-
-* journal mode
-data=journal mode provides full data and metadata journaling. All new data is
-written to the journal first, and then to its final location.
-In the event of a crash, the journal can be replayed, bringing both data and
-metadata into a consistent state. This mode is the slowest except when data
-needs to be read from and written to disk at the same time where it
-outperforms all other modes.
-
-Compatibility
--------------
-
-Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.
-Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as
-Ext2.
-
-
-External Tools
-==============
-See manual pages to learn more.
-
-tune2fs: create a ext3 journal on a ext2 partition with the -j flag.
-mke2fs: create a ext3 partition with the -j flag.
-debugfs: ext2 and ext3 file system debugger.
-ext2online: online (mounted) ext2 and ext3 filesystem resizer
-
-
-References
-==========
-
-kernel source: <file:fs/ext3/>
- <file:fs/jbd/>
-
-programs: http://e2fsprogs.sourceforge.net/
- http://ext2resize.sourceforge.net
-
-useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html
- http://www.ibm.com/developerworks/library/l-fs8/index.html