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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
2Ext3 Filesystem
3===============
4
Jesper Juhlc63ca3c2006-01-09 20:53:57 -08005Ext3 was originally released in September 1999. Written by Stephen Tweedie
6for the 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger,
Linus Torvalds1da177e2005-04-16 15:20:36 -07007Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.
8
Jesper Juhlc63ca3c2006-01-09 20:53:57 -08009Ext3 is the ext2 filesystem enhanced with journalling capabilities.
Linus Torvalds1da177e2005-04-16 15:20:36 -070010
11Options
12=======
13
14When mounting an ext3 filesystem, the following option are accepted:
15(*) == default
16
Pavel Macheke3375ac2009-01-10 00:47:21 +010017ro Mount filesystem read only. Note that ext3 will replay
18 the journal (and thus write to the partition) even when
19 mounted "read only". Mount options "ro,noload" can be
20 used to prevent writes to the filesystem.
21
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080022journal=update Update the ext3 file system's journal to the current
23 format.
Linus Torvalds1da177e2005-04-16 15:20:36 -070024
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080025journal=inum When a journal already exists, this option is ignored.
26 Otherwise, it specifies the number of the inode which
27 will represent the ext3 file system's journal file.
Linus Torvalds1da177e2005-04-16 15:20:36 -070028
Johann Lombardi71b96252006-01-08 01:03:20 -080029journal_dev=devnum When the external journal device's major/minor numbers
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080030 have changed, this option allows the user to specify
31 the new journal location. The journal device is
32 identified through its new major/minor numbers encoded
33 in devnum.
Johann Lombardi71b96252006-01-08 01:03:20 -080034
Eric Sandeendee1d3b2009-11-16 16:50:49 -060035norecovery Don't load the journal on mounting. Note that this forces
36noload mount of inconsistent filesystem, which can lead to
Pavel Macheke3375ac2009-01-10 00:47:21 +010037 various problems.
Linus Torvalds1da177e2005-04-16 15:20:36 -070038
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080039data=journal All data are committed into the journal prior to being
40 written into the main file system.
Linus Torvalds1da177e2005-04-16 15:20:36 -070041
42data=ordered (*) All data are forced directly out to the main file
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080043 system prior to its metadata being committed to the
44 journal.
Linus Torvalds1da177e2005-04-16 15:20:36 -070045
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080046data=writeback Data ordering is not preserved, data may be written
47 into the main file system after its metadata has been
48 committed to the journal.
Linus Torvalds1da177e2005-04-16 15:20:36 -070049
50commit=nrsec (*) Ext3 can be told to sync all its data and metadata
51 every 'nrsec' seconds. The default value is 5 seconds.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080052 This means that if you lose your power, you will lose
53 as much as the latest 5 seconds of work (your
54 filesystem will not be damaged though, thanks to the
55 journaling). This default value (or any low value)
56 will hurt performance, but it's good for data-safety.
57 Setting it to 0 will have the same effect as leaving
58 it at the default (5 seconds).
Linus Torvalds1da177e2005-04-16 15:20:36 -070059 Setting it to very large values will improve
60 performance.
61
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080062barrier=1 This enables/disables barriers. barrier=0 disables
63 it, barrier=1 enables it.
Linus Torvalds1da177e2005-04-16 15:20:36 -070064
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080065orlov (*) This enables the new Orlov block allocator. It is
66 enabled by default.
Linus Torvalds1da177e2005-04-16 15:20:36 -070067
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080068oldalloc This disables the Orlov block allocator and enables
69 the old block allocator. Orlov should have better
70 performance - we'd like to get some feedback if it's
71 the contrary for you.
Linus Torvalds1da177e2005-04-16 15:20:36 -070072
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080073user_xattr Enables Extended User Attributes. Additionally, you
74 need to have extended attribute support enabled in the
75 kernel configuration (CONFIG_EXT3_FS_XATTR). See the
76 attr(5) manual page and http://acl.bestbits.at/ to
77 learn more about extended attributes.
Linus Torvalds1da177e2005-04-16 15:20:36 -070078
Andreas Gruenbacher85b87242005-12-12 00:37:04 -080079nouser_xattr Disables Extended User Attributes.
Linus Torvalds1da177e2005-04-16 15:20:36 -070080
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080081acl Enables POSIX Access Control Lists support.
82 Additionally, you need to have ACL support enabled in
83 the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL).
84 See the acl(5) manual page and http://acl.bestbits.at/
85 for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -070086
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080087noacl This option disables POSIX Access Control List
88 support.
Linus Torvalds1da177e2005-04-16 15:20:36 -070089
90reservation
91
92noreservation
93
Linus Torvalds1da177e2005-04-16 15:20:36 -070094bsddf (*) Make 'df' act like BSD.
95minixdf Make 'df' act like Minix.
96
97check=none Don't do extra checking of bitmaps on mount.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080098nocheck
Linus Torvalds1da177e2005-04-16 15:20:36 -070099
100debug Extra debugging information is sent to syslog.
101
Pavel Macheke3375ac2009-01-10 00:47:21 +0100102errors=remount-ro Remount the filesystem read-only on an error.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103errors=continue Keep going on a filesystem error.
104errors=panic Panic and halt the machine if an error occurs.
Pavel Macheke3375ac2009-01-10 00:47:21 +0100105 (These mount options override the errors behavior
106 specified in the superblock, which can be
107 configured using tune2fs.)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700108
Hidehiro Kawai0e4fb5e2008-10-18 20:27:57 -0700109data_err=ignore(*) Just print an error message if an error occurs
110 in a file data buffer in ordered mode.
111data_err=abort Abort the journal if an error occurs in a file
112 data buffer in ordered mode.
113
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114grpid Give objects the same group ID as their creator.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800115bsdgroups
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116
117nogrpid (*) New objects have the group ID of their creator.
118sysvgroups
119
120resgid=n The group ID which may use the reserved blocks.
121
122resuid=n The user ID which may use the reserved blocks.
123
124sb=n Use alternate superblock at this location.
125
Jan Kara6dbce522009-09-17 17:37:12 +0200126quota These options are ignored by the filesystem. They
127noquota are used only by quota tools to recognize volumes
128grpquota where quota should be turned on. See documentation
129usrquota in the quota-tools package for more details
130 (http://sourceforge.net/projects/linuxquota).
131
132jqfmt=<quota type> These options tell filesystem details about quota
133usrjquota=<file> so that quota information can be properly updated
134grpjquota=<file> during journal replay. They replace the above
135 quota options. See documentation in the quota-tools
136 package for more details
137 (http://sourceforge.net/projects/linuxquota).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700138
Badari Pulavartyade1a292006-06-26 00:25:04 -0700139bh (*) ext3 associates buffer heads to data pages to
140nobh (a) cache disk block mapping information
141 (b) link pages into transaction to provide
142 ordering guarantees.
143 "bh" option forces use of buffer heads.
144 "nobh" option tries to avoid associating buffer
145 heads (supported only for "writeback" mode).
146
Linus Torvalds1da177e2005-04-16 15:20:36 -0700147
148Specification
149=============
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800150Ext3 shares all disk implementation with the ext2 filesystem, and adds
151transactions capabilities to ext2. Journaling is done by the Journaling Block
152Device layer.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153
154Journaling Block Device layer
155-----------------------------
Shaun Zinck73563372007-10-20 02:38:36 +0200156The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed
157to add journaling capabilities to a block device. The ext3 filesystem code
158will inform the JBD of modifications it is performing (called a transaction).
159The journal supports the transactions start and stop, and in case of a crash,
160the journal can replay the transactions to quickly put the partition back into
161a consistent state.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700162
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800163Handles represent a single atomic update to a filesystem. JBD can handle an
164external journal on a block device.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700165
166Data Mode
167---------
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800168There are 3 different data modes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700169
170* writeback mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800171In data=writeback mode, ext3 does not journal data at all. This mode provides
172a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
173mode - metadata journaling. A crash+recovery can cause incorrect data to
174appear in files which were written shortly before the crash. This mode will
175typically provide the best ext3 performance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700176
177* ordered mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800178In data=ordered mode, ext3 only officially journals metadata, but it logically
179groups metadata and data blocks into a single unit called a transaction. When
180it's time to write the new metadata out to disk, the associated data blocks
181are written first. In general, this mode performs slightly slower than
182writeback but significantly faster than journal mode.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700183
184* journal mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800185data=journal mode provides full data and metadata journaling. All new data is
186written to the journal first, and then to its final location.
187In the event of a crash, the journal can be replayed, bringing both data and
188metadata into a consistent state. This mode is the slowest except when data
189needs to be read from and written to disk at the same time where it
Shaun Zinck73563372007-10-20 02:38:36 +0200190outperforms all other modes.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700191
192Compatibility
193-------------
194
195Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800196Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as
197Ext2.
198
Linus Torvalds1da177e2005-04-16 15:20:36 -0700199
200External Tools
201==============
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800202See manual pages to learn more.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700203
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800204tune2fs: create a ext3 journal on a ext2 partition with the -j flag.
205mke2fs: create a ext3 partition with the -j flag.
206debugfs: ext2 and ext3 file system debugger.
Tore Andersone56d5ae2006-01-11 12:17:31 -0800207ext2online: online (mounted) ext2 and ext3 filesystem resizer
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800208
Linus Torvalds1da177e2005-04-16 15:20:36 -0700209
210References
211==========
212
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800213kernel source: <file:fs/ext3/>
214 <file:fs/jbd/>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700215
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800216programs: http://e2fsprogs.sourceforge.net/
Tore Andersone56d5ae2006-01-11 12:17:31 -0800217 http://ext2resize.sourceforge.net
Linus Torvalds1da177e2005-04-16 15:20:36 -0700218
Jody McIntyreab03eca2009-03-12 17:39:23 -0400219useful links: http://www.ibm.com/developerworks/library/l-fs7.html
220 http://www.ibm.com/developerworks/library/l-fs8.html