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view Documentation/filesystems/ext3.txt @ 524:7f8b544237bf

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This is useful if your physical network device is in a utility domain.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Tue Apr 15 15:18:58 2008 +0100 (2008-04-15)
parents 831230e53067
children
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2 Ext3 Filesystem
3 ===============
5 Ext3 was originally released in September 1999. Written by Stephen Tweedie
6 for the 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger,
7 Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.
9 Ext3 is the ext2 filesystem enhanced with journalling capabilities.
11 Options
12 =======
14 When mounting an ext3 filesystem, the following option are accepted:
15 (*) == default
17 journal=update Update the ext3 file system's journal to the current
18 format.
20 journal=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.
24 journal_dev=devnum When the external journal device's major/minor numbers
25 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.
30 noload Don't load the journal on mounting.
32 data=journal All data are committed into the journal prior to being
33 written into the main file system.
35 data=ordered (*) All data are forced directly out to the main file
36 system prior to its metadata being committed to the
37 journal.
39 data=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.
43 commit=nrsec (*) Ext3 can be told to sync all its data and metadata
44 every 'nrsec' seconds. The default value is 5 seconds.
45 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).
52 Setting it to very large values will improve
53 performance.
55 barrier=1 This enables/disables barriers. barrier=0 disables
56 it, barrier=1 enables it.
58 orlov (*) This enables the new Orlov block allocator. It is
59 enabled by default.
61 oldalloc 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.
66 user_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.
72 nouser_xattr Disables Extended User Attributes.
74 acl 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.
80 noacl This option disables POSIX Access Control List
81 support.
83 reservation
85 noreservation
87 bsddf (*) Make 'df' act like BSD.
88 minixdf Make 'df' act like Minix.
90 check=none Don't do extra checking of bitmaps on mount.
91 nocheck
93 debug Extra debugging information is sent to syslog.
95 errors=remount-ro(*) Remount the filesystem read-only on an error.
96 errors=continue Keep going on a filesystem error.
97 errors=panic Panic and halt the machine if an error occurs.
99 grpid Give objects the same group ID as their creator.
100 bsdgroups
102 nogrpid (*) New objects have the group ID of their creator.
103 sysvgroups
105 resgid=n The group ID which may use the reserved blocks.
107 resuid=n The user ID which may use the reserved blocks.
109 sb=n Use alternate superblock at this location.
111 quota
112 noquota
113 grpquota
114 usrquota
116 bh (*) ext3 associates buffer heads to data pages to
117 nobh (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).
125 Specification
126 =============
127 Ext3 shares all disk implementation with the ext2 filesystem, and adds
128 transactions capabilities to ext2. Journaling is done by the Journaling Block
129 Device layer.
131 Journaling Block Device layer
132 -----------------------------
133 The Journaling Block Device layer (JBD) isn't ext3 specific. It was design to
134 add journaling capabilities on a block device. The ext3 filesystem code will
135 inform the JBD of modifications it is performing (called a transaction). The
136 journal supports the transactions start and stop, and in case of crash, the
137 journal can replayed the transactions to put the partition back in a
138 consistent state fast.
140 Handles represent a single atomic update to a filesystem. JBD can handle an
141 external journal on a block device.
143 Data Mode
144 ---------
145 There are 3 different data modes:
147 * writeback mode
148 In data=writeback mode, ext3 does not journal data at all. This mode provides
149 a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
150 mode - metadata journaling. A crash+recovery can cause incorrect data to
151 appear in files which were written shortly before the crash. This mode will
152 typically provide the best ext3 performance.
154 * ordered mode
155 In data=ordered mode, ext3 only officially journals metadata, but it logically
156 groups metadata and data blocks into a single unit called a transaction. When
157 it's time to write the new metadata out to disk, the associated data blocks
158 are written first. In general, this mode performs slightly slower than
159 writeback but significantly faster than journal mode.
161 * journal mode
162 data=journal mode provides full data and metadata journaling. All new data is
163 written to the journal first, and then to its final location.
164 In the event of a crash, the journal can be replayed, bringing both data and
165 metadata into a consistent state. This mode is the slowest except when data
166 needs to be read from and written to disk at the same time where it
167 outperforms all others modes.
169 Compatibility
170 -------------
172 Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.
173 Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as
174 Ext2.
177 External Tools
178 ==============
179 See manual pages to learn more.
181 tune2fs: create a ext3 journal on a ext2 partition with the -j flag.
182 mke2fs: create a ext3 partition with the -j flag.
183 debugfs: ext2 and ext3 file system debugger.
184 ext2online: online (mounted) ext2 and ext3 filesystem resizer
187 References
188 ==========
190 kernel source: <file:fs/ext3/>
191 <file:fs/jbd/>
193 programs: http://e2fsprogs.sourceforge.net/
194 http://ext2resize.sourceforge.net
196 useful links: http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html
197 http://www-106.ibm.com/developerworks/linux/library/l-fs7/
198 http://www-106.ibm.com/developerworks/linux/library/l-fs8/