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.

  orlov		(*)	This enables the new Orlov block allocator. It is
  			enabled by default.

  oldalloc		This disables the Orlov block allocator and enables
  			the old block allocator.  Orlov should have better
  			performance - we'd like to get some feedback if it's
  			the contrary for you.

  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).

  bh		(*)	ext3 associates buffer heads to data pages to
  nobh			(a) cache disk block mapping information
  			(b) link pages into transaction to provide
  			    ordering guarantees.
  			"bh" option forces use of buffer heads.
  			"nobh" option tries to avoid associating buffer
  			heads (supported only for "writeback" mode).

  
  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.html
  		http://www.ibm.com/developerworks/library/l-fs8.html