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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
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080017journal=update Update the ext3 file system's journal to the current
18 format.
Linus Torvalds1da177e2005-04-16 15:20:36 -070019
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080020journal=inum When a journal already exists, this option is ignored.
21 Otherwise, it specifies the number of the inode which
22 will represent the ext3 file system's journal file.
Linus Torvalds1da177e2005-04-16 15:20:36 -070023
Johann Lombardi71b96252006-01-08 01:03:20 -080024journal_dev=devnum When the external journal device's major/minor numbers
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080025 have changed, this option allows the user to specify
26 the new journal location. The journal device is
27 identified through its new major/minor numbers encoded
28 in devnum.
Johann Lombardi71b96252006-01-08 01:03:20 -080029
Linus Torvalds1da177e2005-04-16 15:20:36 -070030noload Don't load the journal on mounting.
31
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080032data=journal All data are committed into the journal prior to being
33 written into the main file system.
Linus Torvalds1da177e2005-04-16 15:20:36 -070034
35data=ordered (*) All data are forced directly out to the main file
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080036 system prior to its metadata being committed to the
37 journal.
Linus Torvalds1da177e2005-04-16 15:20:36 -070038
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080039data=writeback Data ordering is not preserved, data may be written
40 into the main file system after its metadata has been
41 committed to the journal.
Linus Torvalds1da177e2005-04-16 15:20:36 -070042
43commit=nrsec (*) Ext3 can be told to sync all its data and metadata
44 every 'nrsec' seconds. The default value is 5 seconds.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080045 This means that if you lose your power, you will lose
46 as much as the latest 5 seconds of work (your
47 filesystem will not be damaged though, thanks to the
48 journaling). This default value (or any low value)
49 will hurt performance, but it's good for data-safety.
50 Setting it to 0 will have the same effect as leaving
51 it at the default (5 seconds).
Linus Torvalds1da177e2005-04-16 15:20:36 -070052 Setting it to very large values will improve
53 performance.
54
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080055barrier=1 This enables/disables barriers. barrier=0 disables
56 it, barrier=1 enables it.
Linus Torvalds1da177e2005-04-16 15:20:36 -070057
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080058orlov (*) This enables the new Orlov block allocator. It is
59 enabled by default.
Linus Torvalds1da177e2005-04-16 15:20:36 -070060
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080061oldalloc This disables the Orlov block allocator and enables
62 the old block allocator. Orlov should have better
63 performance - we'd like to get some feedback if it's
64 the contrary for you.
Linus Torvalds1da177e2005-04-16 15:20:36 -070065
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080066user_xattr Enables Extended User Attributes. Additionally, you
67 need to have extended attribute support enabled in the
68 kernel configuration (CONFIG_EXT3_FS_XATTR). See the
69 attr(5) manual page and http://acl.bestbits.at/ to
70 learn more about extended attributes.
Linus Torvalds1da177e2005-04-16 15:20:36 -070071
Andreas Gruenbacher85b87242005-12-12 00:37:04 -080072nouser_xattr Disables Extended User Attributes.
Linus Torvalds1da177e2005-04-16 15:20:36 -070073
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080074acl Enables POSIX Access Control Lists support.
75 Additionally, you need to have ACL support enabled in
76 the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL).
77 See the acl(5) manual page and http://acl.bestbits.at/
78 for more information.
Linus Torvalds1da177e2005-04-16 15:20:36 -070079
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080080noacl This option disables POSIX Access Control List
81 support.
Linus Torvalds1da177e2005-04-16 15:20:36 -070082
83reservation
84
85noreservation
86
Linus Torvalds1da177e2005-04-16 15:20:36 -070087bsddf (*) Make 'df' act like BSD.
88minixdf Make 'df' act like Minix.
89
90check=none Don't do extra checking of bitmaps on mount.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -080091nocheck
Linus Torvalds1da177e2005-04-16 15:20:36 -070092
93debug Extra debugging information is sent to syslog.
94
95errors=remount-ro(*) Remount the filesystem read-only on an error.
96errors=continue Keep going on a filesystem error.
97errors=panic Panic and halt the machine if an error occurs.
98
99grpid Give objects the same group ID as their creator.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800100bsdgroups
Linus Torvalds1da177e2005-04-16 15:20:36 -0700101
102nogrpid (*) New objects have the group ID of their creator.
103sysvgroups
104
105resgid=n The group ID which may use the reserved blocks.
106
107resuid=n The user ID which may use the reserved blocks.
108
109sb=n Use alternate superblock at this location.
110
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800111quota
112noquota
Linus Torvalds1da177e2005-04-16 15:20:36 -0700113grpquota
114usrquota
115
Badari Pulavartyade1a292006-06-26 00:25:04 -0700116bh (*) ext3 associates buffer heads to data pages to
117nobh (a) cache disk block mapping information
118 (b) link pages into transaction to provide
119 ordering guarantees.
120 "bh" option forces use of buffer heads.
121 "nobh" option tries to avoid associating buffer
122 heads (supported only for "writeback" mode).
123
Linus Torvalds1da177e2005-04-16 15:20:36 -0700124
125Specification
126=============
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800127Ext3 shares all disk implementation with the ext2 filesystem, and adds
128transactions capabilities to ext2. Journaling is done by the Journaling Block
129Device layer.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700130
131Journaling Block Device layer
132-----------------------------
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800133The Journaling Block Device layer (JBD) isn't ext3 specific. It was design to
134add journaling capabilities on a block device. The ext3 filesystem code will
135inform the JBD of modifications it is performing (called a transaction). The
136journal supports the transactions start and stop, and in case of crash, the
137journal can replayed the transactions to put the partition back in a
138consistent state fast.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700139
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800140Handles represent a single atomic update to a filesystem. JBD can handle an
141external journal on a block device.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700142
143Data Mode
144---------
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800145There are 3 different data modes:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700146
147* writeback mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800148In data=writeback mode, ext3 does not journal data at all. This mode provides
149a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
150mode - metadata journaling. A crash+recovery can cause incorrect data to
151appear in files which were written shortly before the crash. This mode will
152typically provide the best ext3 performance.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153
154* ordered mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800155In data=ordered mode, ext3 only officially journals metadata, but it logically
156groups metadata and data blocks into a single unit called a transaction. When
157it's time to write the new metadata out to disk, the associated data blocks
158are written first. In general, this mode performs slightly slower than
159writeback but significantly faster than journal mode.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700160
161* journal mode
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800162data=journal mode provides full data and metadata journaling. All new data is
163written to the journal first, and then to its final location.
164In the event of a crash, the journal can be replayed, bringing both data and
165metadata into a consistent state. This mode is the slowest except when data
166needs to be read from and written to disk at the same time where it
167outperforms all others modes.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700168
169Compatibility
170-------------
171
172Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800173Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as
174Ext2.
175
Linus Torvalds1da177e2005-04-16 15:20:36 -0700176
177External Tools
178==============
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800179See manual pages to learn more.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700180
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800181tune2fs: create a ext3 journal on a ext2 partition with the -j flag.
182mke2fs: create a ext3 partition with the -j flag.
183debugfs: ext2 and ext3 file system debugger.
Tore Andersone56d5ae2006-01-11 12:17:31 -0800184ext2online: online (mounted) ext2 and ext3 filesystem resizer
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800185
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186
187References
188==========
189
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800190kernel source: <file:fs/ext3/>
191 <file:fs/jbd/>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700192
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800193programs: http://e2fsprogs.sourceforge.net/
Tore Andersone56d5ae2006-01-11 12:17:31 -0800194 http://ext2resize.sourceforge.net
Linus Torvalds1da177e2005-04-16 15:20:36 -0700195
Jesper Juhlc63ca3c2006-01-09 20:53:57 -0800196useful links: http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html
Linus Torvalds1da177e2005-04-16 15:20:36 -0700197 http://www-106.ibm.com/developerworks/linux/library/l-fs7/
198 http://www-106.ibm.com/developerworks/linux/library/l-fs8/