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1
2Ext3 Filesystem
3===============
4
5Ext3 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,
7Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.
8
9Ext3 is the ext2 filesystem enhanced with journalling capabilities.
10
11Options
12=======
13
14When mounting an ext3 filesystem, the following option are accepted:
15(*) == default
16
17ro 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
22journal=update Update the ext3 file system's journal to the current
23 format.
24
25journal=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.
28
29journal_dev=devnum When the external journal device's major/minor numbers
30 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.
34
35norecovery Don't load the journal on mounting. Note that this forces
36noload mount of inconsistent filesystem, which can lead to
37 various problems.
38
39data=journal All data are committed into the journal prior to being
40 written into the main file system.
41
42data=ordered (*) All data are forced directly out to the main file
43 system prior to its metadata being committed to the
44 journal.
45
46data=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.
49
50commit=nrsec (*) Ext3 can be told to sync all its data and metadata
51 every 'nrsec' seconds. The default value is 5 seconds.
52 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).
59 Setting it to very large values will improve
60 performance.
61
62barrier=<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.
75
76orlov (*) This enables the new Orlov block allocator. It is
77 enabled by default.
78
79oldalloc This disables the Orlov block allocator and enables
80 the old block allocator. Orlov should have better
81 performance - we'd like to get some feedback if it's
82 the contrary for you.
83
84user_xattr Enables Extended User Attributes. Additionally, you
85 need to have extended attribute support enabled in the
86 kernel configuration (CONFIG_EXT3_FS_XATTR). See the
87 attr(5) manual page and http://acl.bestbits.at/ to
88 learn more about extended attributes.
89
90nouser_xattr Disables Extended User Attributes.
91
92acl Enables POSIX Access Control Lists support.
93 Additionally, you need to have ACL support enabled in
94 the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL).
95 See the acl(5) manual page and http://acl.bestbits.at/
96 for more information.
97
98noacl This option disables POSIX Access Control List
99 support.
100
101reservation
102
103noreservation
104
105bsddf (*) Make 'df' act like BSD.
106minixdf Make 'df' act like Minix.
107
108check=none Don't do extra checking of bitmaps on mount.
109nocheck
110
111debug Extra debugging information is sent to syslog.
112
113errors=remount-ro Remount the filesystem read-only on an error.
114errors=continue Keep going on a filesystem error.
115errors=panic Panic and halt the machine if an error occurs.
116 (These mount options override the errors behavior
117 specified in the superblock, which can be
118 configured using tune2fs.)
119
120data_err=ignore(*) Just print an error message if an error occurs
121 in a file data buffer in ordered mode.
122data_err=abort Abort the journal if an error occurs in a file
123 data buffer in ordered mode.
124
125grpid Give objects the same group ID as their creator.
126bsdgroups
127
128nogrpid (*) New objects have the group ID of their creator.
129sysvgroups
130
131resgid=n The group ID which may use the reserved blocks.
132
133resuid=n The user ID which may use the reserved blocks.
134
135sb=n Use alternate superblock at this location.
136
137quota These options are ignored by the filesystem. They
138noquota are used only by quota tools to recognize volumes
139grpquota where quota should be turned on. See documentation
140usrquota in the quota-tools package for more details
141 (http://sourceforge.net/projects/linuxquota).
142
143jqfmt=<quota type> These options tell filesystem details about quota
144usrjquota=<file> so that quota information can be properly updated
145grpjquota=<file> during journal replay. They replace the above
146 quota options. See documentation in the quota-tools
147 package for more details
148 (http://sourceforge.net/projects/linuxquota).
149
150Specification
151=============
152Ext3 shares all disk implementation with the ext2 filesystem, and adds
153transactions capabilities to ext2. Journaling is done by the Journaling Block
154Device layer.
155
156Journaling Block Device layer
157-----------------------------
158The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed
159to add journaling capabilities to a block device. The ext3 filesystem code
160will inform the JBD of modifications it is performing (called a transaction).
161The journal supports the transactions start and stop, and in case of a crash,
162the journal can replay the transactions to quickly put the partition back into
163a consistent state.
164
165Handles represent a single atomic update to a filesystem. JBD can handle an
166external journal on a block device.
167
168Data Mode
169---------
170There are 3 different data modes:
171
172* writeback mode
173In data=writeback mode, ext3 does not journal data at all. This mode provides
174a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
175mode - metadata journaling. A crash+recovery can cause incorrect data to
176appear in files which were written shortly before the crash. This mode will
177typically provide the best ext3 performance.
178
179* ordered mode
180In data=ordered mode, ext3 only officially journals metadata, but it logically
181groups metadata and data blocks into a single unit called a transaction. When
182it's time to write the new metadata out to disk, the associated data blocks
183are written first. In general, this mode performs slightly slower than
184writeback but significantly faster than journal mode.
185
186* journal mode
187data=journal mode provides full data and metadata journaling. All new data is
188written to the journal first, and then to its final location.
189In the event of a crash, the journal can be replayed, bringing both data and
190metadata into a consistent state. This mode is the slowest except when data
191needs to be read from and written to disk at the same time where it
192outperforms all other modes.
193
194Compatibility
195-------------
196
197Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.
198Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as
199Ext2.
200
201
202External Tools
203==============
204See manual pages to learn more.
205
206tune2fs: create a ext3 journal on a ext2 partition with the -j flag.
207mke2fs: create a ext3 partition with the -j flag.
208debugfs: ext2 and ext3 file system debugger.
209ext2online: online (mounted) ext2 and ext3 filesystem resizer
210
211
212References
213==========
214
215kernel source: <file:fs/ext3/>
216 <file:fs/jbd/>
217
218programs: http://e2fsprogs.sourceforge.net/
219 http://ext2resize.sourceforge.net
220
221useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html
222 http://www.ibm.com/developerworks/library/l-fs8/index.html
1
2Ext3 Filesystem
3===============
4
5Ext3 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,
7Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.
8
9Ext3 is the ext2 filesystem enhanced with journalling capabilities. The
10filesystem is a subset of ext4 filesystem so use ext4 driver for accessing
11ext3 filesystems.
12