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-rw-r--r--Documentation/filesystems/ext3.txt178
1 files changed, 90 insertions, 88 deletions
diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt
index 22e4040564d5..f4d0de6bac63 100644
--- a/Documentation/filesystems/ext3.txt
+++ b/Documentation/filesystems/ext3.txt
@@ -2,11 +2,11 @@
2Ext3 Filesystem 2Ext3 Filesystem
3=============== 3===============
4 4
5ext3 was originally released in September 1999. Written by Stephen Tweedie 5Ext3 was originally released in September 1999. Written by Stephen Tweedie
6for 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger, 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. 7Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.
8 8
9ext3 is ext2 filesystem enhanced with journalling capabilities. 9Ext3 is the ext2 filesystem enhanced with journalling capabilities.
10 10
11Options 11Options
12======= 12=======
@@ -14,69 +14,71 @@ Options
14When mounting an ext3 filesystem, the following option are accepted: 14When mounting an ext3 filesystem, the following option are accepted:
15(*) == default 15(*) == default
16 16
17jounal=update Update the ext3 file system's journal to the 17journal=update Update the ext3 file system's journal to the current
18 current format. 18 format.
19 19
20journal=inum When a journal already exists, this option is 20journal=inum When a journal already exists, this option is ignored.
21 ignored. Otherwise, it specifies the number of 21 Otherwise, it specifies the number of the inode which
22 the inode which will represent the ext3 file 22 will represent the ext3 file system's journal file.
23 system's journal file.
24 23
25journal_dev=devnum When the external journal device's major/minor numbers 24journal_dev=devnum When the external journal device's major/minor numbers
26 have changed, this option allows to specify the new 25 have changed, this option allows the user to specify
27 journal location. The journal device is identified 26 the new journal location. The journal device is
28 through its new major/minor numbers encoded in devnum. 27 identified through its new major/minor numbers encoded
28 in devnum.
29 29
30noload Don't load the journal on mounting. 30noload Don't load the journal on mounting.
31 31
32data=journal All data are committed into the journal prior 32data=journal All data are committed into the journal prior to being
33 to being written into the main file system. 33 written into the main file system.
34 34
35data=ordered (*) All data are forced directly out to the main file 35data=ordered (*) All data are forced directly out to the main file
36 system prior to its metadata being committed to 36 system prior to its metadata being committed to the
37 the journal. 37 journal.
38 38
39data=writeback Data ordering is not preserved, data may be 39data=writeback Data ordering is not preserved, data may be written
40 written into the main file system after its 40 into the main file system after its metadata has been
41 metadata has been committed to the journal. 41 committed to the journal.
42 42
43commit=nrsec (*) Ext3 can be told to sync all its data and metadata 43commit=nrsec (*) Ext3 can be told to sync all its data and metadata
44 every 'nrsec' seconds. The default value is 5 seconds. 44 every 'nrsec' seconds. The default value is 5 seconds.
45 This means that if you lose your power, you will lose, 45 This means that if you lose your power, you will lose
46 as much, the latest 5 seconds of work (your filesystem 46 as much as the latest 5 seconds of work (your
47 will not be damaged though, thanks to journaling). This 47 filesystem will not be damaged though, thanks to the
48 default value (or any low value) will hurt performance, 48 journaling). This default value (or any low value)
49 but it's good for data-safety. Setting it to 0 will 49 will hurt performance, but it's good for data-safety.
50 have the same effect than leaving the default 5 sec. 50 Setting it to 0 will have the same effect as leaving
51 it at the default (5 seconds).
51 Setting it to very large values will improve 52 Setting it to very large values will improve
52 performance. 53 performance.
53 54
54barrier=1 This enables/disables barriers. barrier=0 disables it, 55barrier=1 This enables/disables barriers. barrier=0 disables
55 barrier=1 enables it. 56 it, barrier=1 enables it.
56 57
57orlov (*) This enables the new Orlov block allocator. It's enabled 58orlov (*) This enables the new Orlov block allocator. It is
58 by default. 59 enabled by default.
59 60
60oldalloc This disables the Orlov block allocator and enables the 61oldalloc This disables the Orlov block allocator and enables
61 old block allocator. Orlov should have better performance, 62 the old block allocator. Orlov should have better
62 we'd like to get some feedback if it's the contrary for 63 performance - we'd like to get some feedback if it's
63 you. 64 the contrary for you.
64 65
65user_xattr Enables Extended User Attributes. Additionally, you need 66user_xattr Enables Extended User Attributes. Additionally, you
66 to have extended attribute support enabled in the kernel 67 need to have extended attribute support enabled in the
67 configuration (CONFIG_EXT3_FS_XATTR). See the attr(5) 68 kernel configuration (CONFIG_EXT3_FS_XATTR). See the
68 manual page and http://acl.bestbits.at to learn more 69 attr(5) manual page and http://acl.bestbits.at/ to
69 about extended attributes. 70 learn more about extended attributes.
70 71
71nouser_xattr Disables Extended User Attributes. 72nouser_xattr Disables Extended User Attributes.
72 73
73acl Enables POSIX Access Control Lists support. Additionally, 74acl Enables POSIX Access Control Lists support.
74 you need to have ACL support enabled in the kernel 75 Additionally, you need to have ACL support enabled in
75 configuration (CONFIG_EXT3_FS_POSIX_ACL). See the acl(5) 76 the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL).
76 manual page and http://acl.bestbits.at for more 77 See the acl(5) manual page and http://acl.bestbits.at/
77 information. 78 for more information.
78 79
79noacl This option disables POSIX Access Control List support. 80noacl This option disables POSIX Access Control List
81 support.
80 82
81reservation 83reservation
82 84
@@ -88,7 +90,7 @@ bsddf (*) Make 'df' act like BSD.
88minixdf Make 'df' act like Minix. 90minixdf Make 'df' act like Minix.
89 91
90check=none Don't do extra checking of bitmaps on mount. 92check=none Don't do extra checking of bitmaps on mount.
91nocheck 93nocheck
92 94
93debug Extra debugging information is sent to syslog. 95debug Extra debugging information is sent to syslog.
94 96
@@ -97,7 +99,7 @@ errors=continue Keep going on a filesystem error.
97errors=panic Panic and halt the machine if an error occurs. 99errors=panic Panic and halt the machine if an error occurs.
98 100
99grpid Give objects the same group ID as their creator. 101grpid Give objects the same group ID as their creator.
100bsdgroups 102bsdgroups
101 103
102nogrpid (*) New objects have the group ID of their creator. 104nogrpid (*) New objects have the group ID of their creator.
103sysvgroups 105sysvgroups
@@ -108,81 +110,81 @@ resuid=n The user ID which may use the reserved blocks.
108 110
109sb=n Use alternate superblock at this location. 111sb=n Use alternate superblock at this location.
110 112
111quota Quota options are currently silently ignored. 113quota
112noquota (see fs/ext3/super.c, line 594) 114noquota
113grpquota 115grpquota
114usrquota 116usrquota
115 117
116 118
117Specification 119Specification
118============= 120=============
119ext3 shares all disk implementation with ext2 filesystem, and add 121Ext3 shares all disk implementation with the ext2 filesystem, and adds
120transactions capabilities to ext2. Journaling is done by the 122transactions capabilities to ext2. Journaling is done by the Journaling Block
121Journaling block device layer. 123Device layer.
122 124
123Journaling Block Device layer 125Journaling Block Device layer
124----------------------------- 126-----------------------------
125The Journaling Block Device layer (JBD) isn't ext3 specific. It was 127The Journaling Block Device layer (JBD) isn't ext3 specific. It was design to
126design to add journaling capabilities on a block device. The ext3 128add journaling capabilities on a block device. The ext3 filesystem code will
127filesystem code will inform the JBD of modifications it is performing 129inform the JBD of modifications it is performing (called a transaction). The
128(Call a transaction). the journal support the transactions start and 130journal supports the transactions start and stop, and in case of crash, the
129stop, and in case of crash, the journal can replayed the transactions 131journal can replayed the transactions to put the partition back in a
130to put the partition on a consistent state fastly. 132consistent state fast.
131 133
132handles represent a single atomic update to a filesystem. JBD can 134Handles represent a single atomic update to a filesystem. JBD can handle an
133handle external journal on a block device. 135external journal on a block device.
134 136
135Data Mode 137Data Mode
136--------- 138---------
137There's 3 different data modes: 139There are 3 different data modes:
138 140
139* writeback mode 141* writeback mode
140In data=writeback mode, ext3 does not journal data at all. This mode 142In data=writeback mode, ext3 does not journal data at all. This mode provides
141provides a similar level of journaling as XFS, JFS, and ReiserFS in its 143a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
142default mode - metadata journaling. A crash+recovery can cause 144mode - metadata journaling. A crash+recovery can cause incorrect data to
143incorrect data to appear in files which were written shortly before the 145appear in files which were written shortly before the crash. This mode will
144crash. This mode will typically provide the best ext3 performance. 146typically provide the best ext3 performance.
145 147
146* ordered mode 148* ordered mode
147In data=ordered mode, ext3 only officially journals metadata, but it 149In data=ordered mode, ext3 only officially journals metadata, but it logically
148logically groups metadata and data blocks into a single unit called a 150groups metadata and data blocks into a single unit called a transaction. When
149transaction. When it's time to write the new metadata out to disk, the 151it's time to write the new metadata out to disk, the associated data blocks
150associated data blocks are written first. In general, this mode 152are written first. In general, this mode performs slightly slower than
151perform slightly slower than writeback but significantly faster than 153writeback but significantly faster than journal mode.
152journal mode.
153 154
154* journal mode 155* journal mode
155data=journal mode provides full data and metadata journaling. All new 156data=journal mode provides full data and metadata journaling. All new data is
156data is written to the journal first, and then to its final location. 157written to the journal first, and then to its final location.
157In the event of a crash, the journal can be replayed, bringing both 158In the event of a crash, the journal can be replayed, bringing both data and
158data and metadata into a consistent state. This mode is the slowest 159metadata into a consistent state. This mode is the slowest except when data
159except when data needs to be read from and written to disk at the same 160needs to be read from and written to disk at the same time where it
160time where it outperform all others mode. 161outperforms all others modes.
161 162
162Compatibility 163Compatibility
163------------- 164-------------
164 165
165Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. 166Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.
166Ext3 is fully compatible with Ext2. Ext3 partitions can easily be 167Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as
167mounted as Ext2. 168Ext2.
169
168 170
169External Tools 171External Tools
170============== 172==============
171see manual pages to know more. 173See manual pages to learn more.
174
175tune2fs: create a ext3 journal on a ext2 partition with the -j flag.
176mke2fs: create a ext3 partition with the -j flag.
177debugfs: ext2 and ext3 file system debugger.
172 178
173tune2fs: create a ext3 journal on a ext2 partition with the -j flags
174mke2fs: create a ext3 partition with the -j flags
175debugfs: ext2 and ext3 file system debugger
176 179
177References 180References
178========== 181==========
179 182
180kernel source: file:/usr/src/linux/fs/ext3 183kernel source: <file:fs/ext3/>
181 file:/usr/src/linux/fs/jbd 184 <file:fs/jbd/>
182 185
183programs: http://e2fsprogs.sourceforge.net 186programs: http://e2fsprogs.sourceforge.net/
184 187
185useful link: 188useful links: http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html
186 http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html
187 http://www-106.ibm.com/developerworks/linux/library/l-fs7/ 189 http://www-106.ibm.com/developerworks/linux/library/l-fs7/
188 http://www-106.ibm.com/developerworks/linux/library/l-fs8/ 190 http://www-106.ibm.com/developerworks/linux/library/l-fs8/