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1da177e4 LT |
1 | |
2 | Ext3 Filesystem | |
3 | =============== | |
4 | ||
c63ca3c8 JJ |
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, | |
1da177e4 LT |
7 | Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie. |
8 | ||
c63ca3c8 | 9 | Ext3 is the ext2 filesystem enhanced with journalling capabilities. |
1da177e4 LT |
10 | |
11 | Options | |
12 | ======= | |
13 | ||
14 | When mounting an ext3 filesystem, the following option are accepted: | |
15 | (*) == default | |
16 | ||
c63ca3c8 JJ |
17 | journal=update Update the ext3 file system's journal to the current |
18 | format. | |
1da177e4 | 19 | |
c63ca3c8 JJ |
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. | |
1da177e4 | 23 | |
71b96257 | 24 | journal_dev=devnum When the external journal device's major/minor numbers |
c63ca3c8 JJ |
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. | |
71b96257 | 29 | |
1da177e4 LT |
30 | noload Don't load the journal on mounting. |
31 | ||
c63ca3c8 JJ |
32 | data=journal All data are committed into the journal prior to being |
33 | written into the main file system. | |
1da177e4 LT |
34 | |
35 | data=ordered (*) All data are forced directly out to the main file | |
c63ca3c8 JJ |
36 | system prior to its metadata being committed to the |
37 | journal. | |
1da177e4 | 38 | |
c63ca3c8 JJ |
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. | |
1da177e4 LT |
42 | |
43 | commit=nrsec (*) Ext3 can be told to sync all its data and metadata | |
44 | every 'nrsec' seconds. The default value is 5 seconds. | |
c63ca3c8 JJ |
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). | |
1da177e4 LT |
52 | Setting it to very large values will improve |
53 | performance. | |
54 | ||
c63ca3c8 JJ |
55 | barrier=1 This enables/disables barriers. barrier=0 disables |
56 | it, barrier=1 enables it. | |
1da177e4 | 57 | |
c63ca3c8 JJ |
58 | orlov (*) This enables the new Orlov block allocator. It is |
59 | enabled by default. | |
1da177e4 | 60 | |
c63ca3c8 JJ |
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. | |
1da177e4 | 65 | |
c63ca3c8 JJ |
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. | |
85b87242 AG |
71 | |
72 | nouser_xattr Disables Extended User Attributes. | |
73 | ||
c63ca3c8 JJ |
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. | |
1da177e4 | 79 | |
c63ca3c8 JJ |
80 | noacl This option disables POSIX Access Control List |
81 | support. | |
1da177e4 LT |
82 | |
83 | reservation | |
84 | ||
85 | noreservation | |
86 | ||
1da177e4 LT |
87 | bsddf (*) Make 'df' act like BSD. |
88 | minixdf Make 'df' act like Minix. | |
89 | ||
90 | check=none Don't do extra checking of bitmaps on mount. | |
c63ca3c8 | 91 | nocheck |
1da177e4 LT |
92 | |
93 | debug Extra debugging information is sent to syslog. | |
94 | ||
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. | |
98 | ||
99 | grpid Give objects the same group ID as their creator. | |
c63ca3c8 | 100 | bsdgroups |
1da177e4 LT |
101 | |
102 | nogrpid (*) New objects have the group ID of their creator. | |
103 | sysvgroups | |
104 | ||
105 | resgid=n The group ID which may use the reserved blocks. | |
106 | ||
107 | resuid=n The user ID which may use the reserved blocks. | |
108 | ||
109 | sb=n Use alternate superblock at this location. | |
110 | ||
c63ca3c8 JJ |
111 | quota |
112 | noquota | |
1da177e4 LT |
113 | grpquota |
114 | usrquota | |
115 | ||
ade1a29e BP |
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). | |
123 | ||
1da177e4 LT |
124 | |
125 | Specification | |
126 | ============= | |
c63ca3c8 JJ |
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. | |
1da177e4 LT |
130 | |
131 | Journaling Block Device layer | |
132 | ----------------------------- | |
c63ca3c8 JJ |
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. | |
1da177e4 | 139 | |
c63ca3c8 JJ |
140 | Handles represent a single atomic update to a filesystem. JBD can handle an |
141 | external journal on a block device. | |
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142 | |
143 | Data Mode | |
144 | --------- | |
c63ca3c8 | 145 | There are 3 different data modes: |
1da177e4 LT |
146 | |
147 | * writeback mode | |
c63ca3c8 JJ |
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. | |
1da177e4 LT |
153 | |
154 | * ordered mode | |
c63ca3c8 JJ |
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. | |
1da177e4 LT |
160 | |
161 | * journal mode | |
c63ca3c8 JJ |
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. | |
1da177e4 LT |
168 | |
169 | Compatibility | |
170 | ------------- | |
171 | ||
172 | Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. | |
c63ca3c8 JJ |
173 | Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as |
174 | Ext2. | |
175 | ||
1da177e4 LT |
176 | |
177 | External Tools | |
178 | ============== | |
c63ca3c8 JJ |
179 | See manual pages to learn more. |
180 | ||
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. | |
e56d5ae3 | 184 | ext2online: online (mounted) ext2 and ext3 filesystem resizer |
1da177e4 | 185 | |
1da177e4 LT |
186 | |
187 | References | |
188 | ========== | |
189 | ||
c63ca3c8 JJ |
190 | kernel source: <file:fs/ext3/> |
191 | <file:fs/jbd/> | |
1da177e4 | 192 | |
c63ca3c8 | 193 | programs: http://e2fsprogs.sourceforge.net/ |
e56d5ae3 | 194 | http://ext2resize.sourceforge.net |
1da177e4 | 195 | |
c63ca3c8 | 196 | useful links: http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html |
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197 | http://www-106.ibm.com/developerworks/linux/library/l-fs7/ |
198 | http://www-106.ibm.com/developerworks/linux/library/l-fs8/ |