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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 | ||
e3375ac7 PM |
17 | ro 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 | ||
c63ca3c8 JJ |
22 | journal=update Update the ext3 file system's journal to the current |
23 | format. | |
1da177e4 | 24 | |
c63ca3c8 JJ |
25 | journal=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. | |
1da177e4 | 28 | |
71b96257 | 29 | journal_dev=devnum When the external journal device's major/minor numbers |
c63ca3c8 JJ |
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. | |
71b96257 | 34 | |
dee1d3b6 ES |
35 | norecovery Don't load the journal on mounting. Note that this forces |
36 | noload mount of inconsistent filesystem, which can lead to | |
e3375ac7 | 37 | various problems. |
1da177e4 | 38 | |
c63ca3c8 JJ |
39 | data=journal All data are committed into the journal prior to being |
40 | written into the main file system. | |
1da177e4 LT |
41 | |
42 | data=ordered (*) All data are forced directly out to the main file | |
c63ca3c8 JJ |
43 | system prior to its metadata being committed to the |
44 | journal. | |
1da177e4 | 45 | |
c63ca3c8 JJ |
46 | data=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. | |
1da177e4 LT |
49 | |
50 | commit=nrsec (*) Ext3 can be told to sync all its data and metadata | |
51 | every 'nrsec' seconds. The default value is 5 seconds. | |
c63ca3c8 JJ |
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). | |
1da177e4 LT |
59 | Setting it to very large values will improve |
60 | performance. | |
61 | ||
0636c73e ES |
62 | barrier=<0(*)|1> This enables/disables the use of write barriers in |
63 | barrier the jbd code. barrier=0 disables, barrier=1 enables. | |
64 | nobarrier (*) 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. | |
1da177e4 | 75 | |
c63ca3c8 JJ |
76 | orlov (*) This enables the new Orlov block allocator. It is |
77 | enabled by default. | |
1da177e4 | 78 | |
c63ca3c8 JJ |
79 | oldalloc 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. | |
1da177e4 | 83 | |
c63ca3c8 JJ |
84 | user_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. | |
85b87242 AG |
89 | |
90 | nouser_xattr Disables Extended User Attributes. | |
91 | ||
c63ca3c8 JJ |
92 | acl 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. | |
1da177e4 | 97 | |
c63ca3c8 JJ |
98 | noacl This option disables POSIX Access Control List |
99 | support. | |
1da177e4 LT |
100 | |
101 | reservation | |
102 | ||
103 | noreservation | |
104 | ||
1da177e4 LT |
105 | bsddf (*) Make 'df' act like BSD. |
106 | minixdf Make 'df' act like Minix. | |
107 | ||
108 | check=none Don't do extra checking of bitmaps on mount. | |
c63ca3c8 | 109 | nocheck |
1da177e4 LT |
110 | |
111 | debug Extra debugging information is sent to syslog. | |
112 | ||
e3375ac7 | 113 | errors=remount-ro Remount the filesystem read-only on an error. |
1da177e4 LT |
114 | errors=continue Keep going on a filesystem error. |
115 | errors=panic Panic and halt the machine if an error occurs. | |
e3375ac7 PM |
116 | (These mount options override the errors behavior |
117 | specified in the superblock, which can be | |
118 | configured using tune2fs.) | |
1da177e4 | 119 | |
0e4fb5e2 HK |
120 | data_err=ignore(*) Just print an error message if an error occurs |
121 | in a file data buffer in ordered mode. | |
122 | data_err=abort Abort the journal if an error occurs in a file | |
123 | data buffer in ordered mode. | |
124 | ||
1da177e4 | 125 | grpid Give objects the same group ID as their creator. |
c63ca3c8 | 126 | bsdgroups |
1da177e4 LT |
127 | |
128 | nogrpid (*) New objects have the group ID of their creator. | |
129 | sysvgroups | |
130 | ||
131 | resgid=n The group ID which may use the reserved blocks. | |
132 | ||
133 | resuid=n The user ID which may use the reserved blocks. | |
134 | ||
135 | sb=n Use alternate superblock at this location. | |
136 | ||
6dbce521 JK |
137 | quota These options are ignored by the filesystem. They |
138 | noquota are used only by quota tools to recognize volumes | |
139 | grpquota where quota should be turned on. See documentation | |
140 | usrquota in the quota-tools package for more details | |
141 | (http://sourceforge.net/projects/linuxquota). | |
142 | ||
143 | jqfmt=<quota type> These options tell filesystem details about quota | |
144 | usrjquota=<file> so that quota information can be properly updated | |
145 | grpjquota=<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). | |
1da177e4 | 149 | |
ade1a29e BP |
150 | bh (*) ext3 associates buffer heads to data pages to |
151 | nobh (a) cache disk block mapping information | |
152 | (b) link pages into transaction to provide | |
153 | ordering guarantees. | |
154 | "bh" option forces use of buffer heads. | |
155 | "nobh" option tries to avoid associating buffer | |
156 | heads (supported only for "writeback" mode). | |
157 | ||
1da177e4 LT |
158 | |
159 | Specification | |
160 | ============= | |
c63ca3c8 JJ |
161 | Ext3 shares all disk implementation with the ext2 filesystem, and adds |
162 | transactions capabilities to ext2. Journaling is done by the Journaling Block | |
163 | Device layer. | |
1da177e4 LT |
164 | |
165 | Journaling Block Device layer | |
166 | ----------------------------- | |
7356337b SZ |
167 | The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed |
168 | to add journaling capabilities to a block device. The ext3 filesystem code | |
169 | will inform the JBD of modifications it is performing (called a transaction). | |
170 | The journal supports the transactions start and stop, and in case of a crash, | |
171 | the journal can replay the transactions to quickly put the partition back into | |
172 | a consistent state. | |
1da177e4 | 173 | |
c63ca3c8 JJ |
174 | Handles represent a single atomic update to a filesystem. JBD can handle an |
175 | external journal on a block device. | |
1da177e4 LT |
176 | |
177 | Data Mode | |
178 | --------- | |
c63ca3c8 | 179 | There are 3 different data modes: |
1da177e4 LT |
180 | |
181 | * writeback mode | |
c63ca3c8 JJ |
182 | In data=writeback mode, ext3 does not journal data at all. This mode provides |
183 | a similar level of journaling as that of XFS, JFS, and ReiserFS in its default | |
184 | mode - metadata journaling. A crash+recovery can cause incorrect data to | |
185 | appear in files which were written shortly before the crash. This mode will | |
186 | typically provide the best ext3 performance. | |
1da177e4 LT |
187 | |
188 | * ordered mode | |
c63ca3c8 JJ |
189 | In data=ordered mode, ext3 only officially journals metadata, but it logically |
190 | groups metadata and data blocks into a single unit called a transaction. When | |
191 | it's time to write the new metadata out to disk, the associated data blocks | |
192 | are written first. In general, this mode performs slightly slower than | |
193 | writeback but significantly faster than journal mode. | |
1da177e4 LT |
194 | |
195 | * journal mode | |
c63ca3c8 JJ |
196 | data=journal mode provides full data and metadata journaling. All new data is |
197 | written to the journal first, and then to its final location. | |
198 | In the event of a crash, the journal can be replayed, bringing both data and | |
199 | metadata into a consistent state. This mode is the slowest except when data | |
200 | needs to be read from and written to disk at the same time where it | |
7356337b | 201 | outperforms all other modes. |
1da177e4 LT |
202 | |
203 | Compatibility | |
204 | ------------- | |
205 | ||
206 | Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. | |
c63ca3c8 JJ |
207 | Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as |
208 | Ext2. | |
209 | ||
1da177e4 LT |
210 | |
211 | External Tools | |
212 | ============== | |
c63ca3c8 JJ |
213 | See manual pages to learn more. |
214 | ||
215 | tune2fs: create a ext3 journal on a ext2 partition with the -j flag. | |
216 | mke2fs: create a ext3 partition with the -j flag. | |
217 | debugfs: ext2 and ext3 file system debugger. | |
e56d5ae3 | 218 | ext2online: online (mounted) ext2 and ext3 filesystem resizer |
1da177e4 | 219 | |
1da177e4 LT |
220 | |
221 | References | |
222 | ========== | |
223 | ||
c63ca3c8 JJ |
224 | kernel source: <file:fs/ext3/> |
225 | <file:fs/jbd/> | |
1da177e4 | 226 | |
c63ca3c8 | 227 | programs: http://e2fsprogs.sourceforge.net/ |
e56d5ae3 | 228 | http://ext2resize.sourceforge.net |
1da177e4 | 229 | |
ab03eca8 JM |
230 | useful links: http://www.ibm.com/developerworks/library/l-fs7.html |
231 | http://www.ibm.com/developerworks/library/l-fs8.html |