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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
Eric Sandeen0636c732010-04-30 11:09:34 -050062barrier=<0(*)|1> This enables/disables the use of write barriers in
63barrier the jbd code. barrier=0 disables, barrier=1 enables.
64nobarrier (*) This also requires an IO stack which can support
65 barriers, and if jbd gets an error on a barrier
66 write, it will disable again with a warning.
67 Write barriers enforce proper on-disk ordering
68 of journal commits, making volatile disk write caches
69 safe to use, at some performance penalty. If
70 your disks are battery-backed in one way or another,
71 disabling barriers may safely improve performance.
72 The mount options "barrier" and "nobarrier" can
73 also be used to enable or disable barriers, for
74 consistency with other ext3 mount options.
Linus Torvalds1da177e2005-04-16 15:20:36 -070075
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080076user_xattr Enables Extended User Attributes. Additionally, you
77 need to have extended attribute support enabled in the
78 kernel configuration (CONFIG_EXT3_FS_XATTR). See the
79 attr(5) manual page and http://acl.bestbits.at/ to
80 learn more about extended attributes.
Linus Torvalds1da177e2005-04-16 15:20:36 -070081
Andreas Gruenbacher85b87242005-12-12 00:37:04 -080082nouser_xattr Disables Extended User Attributes.
Linus Torvalds1da177e2005-04-16 15:20:36 -070083
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080084acl Enables POSIX Access Control Lists support.
85 Additionally, you need to have ACL support enabled in
86 the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL).
87 See the acl(5) manual page and http://acl.bestbits.at/
88 for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -070089
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080090noacl This option disables POSIX Access Control List
91 support.
Linus Torvalds1da177e2005-04-16 15:20:36 -070092
93reservation
94
95noreservation
96
Linus Torvalds1da177e2005-04-16 15:20:36 -070097bsddf (*) Make 'df' act like BSD.
98minixdf Make 'df' act like Minix.
99
100check=none Don't do extra checking of bitmaps on mount.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800101nocheck
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102
103debug Extra debugging information is sent to syslog.
104
Pavel Macheke3375ac2009-01-10 00:47:21 +0100105errors=remount-ro Remount the filesystem read-only on an error.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700106errors=continue Keep going on a filesystem error.
107errors=panic Panic and halt the machine if an error occurs.
Pavel Macheke3375ac2009-01-10 00:47:21 +0100108 (These mount options override the errors behavior
109 specified in the superblock, which can be
110 configured using tune2fs.)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111
Hidehiro Kawai0e4fb5e2008-10-18 20:27:57 -0700112data_err=ignore(*) Just print an error message if an error occurs
113 in a file data buffer in ordered mode.
114data_err=abort Abort the journal if an error occurs in a file
115 data buffer in ordered mode.
116
Linus Torvalds1da177e2005-04-16 15:20:36 -0700117grpid Give objects the same group ID as their creator.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800118bsdgroups
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119
120nogrpid (*) New objects have the group ID of their creator.
121sysvgroups
122
123resgid=n The group ID which may use the reserved blocks.
124
125resuid=n The user ID which may use the reserved blocks.
126
127sb=n Use alternate superblock at this location.
128
Jan Kara6dbce522009-09-17 17:37:12 +0200129quota These options are ignored by the filesystem. They
130noquota are used only by quota tools to recognize volumes
131grpquota where quota should be turned on. See documentation
132usrquota in the quota-tools package for more details
133 (http://sourceforge.net/projects/linuxquota).
134
135jqfmt=<quota type> These options tell filesystem details about quota
136usrjquota=<file> so that quota information can be properly updated
137grpjquota=<file> during journal replay. They replace the above
138 quota options. See documentation in the quota-tools
139 package for more details
140 (http://sourceforge.net/projects/linuxquota).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700141
Linus Torvalds1da177e2005-04-16 15:20:36 -0700142Specification
143=============
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800144Ext3 shares all disk implementation with the ext2 filesystem, and adds
145transactions capabilities to ext2. Journaling is done by the Journaling Block
146Device layer.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700147
148Journaling Block Device layer
149-----------------------------
Shaun Zinck73563372007-10-20 02:38:36 +0200150The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed
151to add journaling capabilities to a block device. The ext3 filesystem code
152will inform the JBD of modifications it is performing (called a transaction).
153The journal supports the transactions start and stop, and in case of a crash,
154the journal can replay the transactions to quickly put the partition back into
155a consistent state.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700156
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800157Handles represent a single atomic update to a filesystem. JBD can handle an
158external journal on a block device.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700159
160Data Mode
161---------
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800162There are 3 different data modes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700163
164* writeback mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800165In data=writeback mode, ext3 does not journal data at all. This mode provides
166a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
167mode - metadata journaling. A crash+recovery can cause incorrect data to
168appear in files which were written shortly before the crash. This mode will
169typically provide the best ext3 performance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700170
171* ordered mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800172In data=ordered mode, ext3 only officially journals metadata, but it logically
173groups metadata and data blocks into a single unit called a transaction. When
174it's time to write the new metadata out to disk, the associated data blocks
175are written first. In general, this mode performs slightly slower than
176writeback but significantly faster than journal mode.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177
178* journal mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800179data=journal mode provides full data and metadata journaling. All new data is
180written to the journal first, and then to its final location.
181In the event of a crash, the journal can be replayed, bringing both data and
182metadata into a consistent state. This mode is the slowest except when data
183needs to be read from and written to disk at the same time where it
Shaun Zinck73563372007-10-20 02:38:36 +0200184outperforms all other modes.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700185
186Compatibility
187-------------
188
189Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800190Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as
191Ext2.
192
Linus Torvalds1da177e2005-04-16 15:20:36 -0700193
194External Tools
195==============
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800196See manual pages to learn more.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700197
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800198tune2fs: create a ext3 journal on a ext2 partition with the -j flag.
199mke2fs: create a ext3 partition with the -j flag.
200debugfs: ext2 and ext3 file system debugger.
Tore Andersone56d5ae2006-01-11 12:17:31 -0800201ext2online: online (mounted) ext2 and ext3 filesystem resizer
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800202
Linus Torvalds1da177e2005-04-16 15:20:36 -0700203
204References
205==========
206
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800207kernel source: <file:fs/ext3/>
208 <file:fs/jbd/>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700209
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800210programs: http://e2fsprogs.sourceforge.net/
Tore Andersone56d5ae2006-01-11 12:17:31 -0800211 http://ext2resize.sourceforge.net
Linus Torvalds1da177e2005-04-16 15:20:36 -0700212
Wang Sheng-Hui2b76aa02011-07-23 09:08:49 +0800213useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html
214 http://www.ibm.com/developerworks/library/l-fs8/index.html