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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
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Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+
+Ext3 Filesystem
+===============
+
+ext3 was originally released in September 1999. Written by Stephen Tweedie
+for 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 ext2 filesystem enhanced with journalling capabilities.
+
+Options
+=======
+
+When mounting an ext3 filesystem, the following option are accepted:
+(*) == default
+
+jounal=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.
+
+noload Don't load the journal on mounting.
+
+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, the latest 5 seconds of work (your filesystem
+ will not be damaged though, thanks to 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 than leaving the default 5 sec.
+ Setting it to very large values will improve
+ performance.
+
+barrier=1 This enables/disables barriers. barrier=0 disables it,
+ barrier=1 enables it.
+
+orlov (*) This enables the new Orlov block allocator. It's 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 POSIX Extended Attributes. It's enabled by
+ default, however you need to confifure its support
+ (CONFIG_EXT3_FS_XATTR). This is neccesary if you want
+ to use POSIX Acces Control Lists support. You can visit
+ http://acl.bestbits.at to know more about POSIX Extended
+ attributes.
+
+nouser_xattr Disables POSIX Extended Attributes.
+
+acl (*) Enables POSIX Access Control Lists support. This is
+ enabled by default, however you need to configure
+ its support (CONFIG_EXT3_FS_POSIX_ACL). If you want
+ to know more about ACLs visit http://acl.bestbits.at
+
+noacl This option disables POSIX Access Control List support.
+
+reservation
+
+noreservation
+
+resize=
+
+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.
+
+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 Quota options are currently silently ignored.
+noquota (see fs/ext3/super.c, line 594)
+grpquota
+usrquota
+
+
+Specification
+=============
+ext3 shares all disk implementation with ext2 filesystem, and add
+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
+design to add journaling capabilities on a block device. The ext3
+filesystem code will inform the JBD of modifications it is performing
+(Call a transaction). the journal support the transactions start and
+stop, and in case of crash, the journal can replayed the transactions
+to put the partition on a consistent state fastly.
+
+handles represent a single atomic update to a filesystem. JBD can
+handle external journal on a block device.
+
+Data Mode
+---------
+There's 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 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
+perform 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 outperform all others mode.
+
+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 know more.
+
+tune2fs: create a ext3 journal on a ext2 partition with the -j flags
+mke2fs: create a ext3 partition with the -j flags
+debugfs: ext2 and ext3 file system debugger
+
+References
+==========
+
+kernel source: file:/usr/src/linux/fs/ext3
+ file:/usr/src/linux/fs/jbd
+
+programs: http://e2fsprogs.sourceforge.net
+
+useful link:
+ http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html
+ http://www-106.ibm.com/developerworks/linux/library/l-fs7/
+ http://www-106.ibm.com/developerworks/linux/library/l-fs8/