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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 | |
e3375ac7 PM |
35 | noload Don't load the journal on mounting. Note that this forces |
36 | mount of inconsistent filesystem, which can lead to | |
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 | ||
c63ca3c8 JJ |
62 | barrier=1 This enables/disables barriers. barrier=0 disables |
63 | it, barrier=1 enables it. | |
1da177e4 | 64 | |
c63ca3c8 JJ |
65 | orlov (*) This enables the new Orlov block allocator. It is |
66 | enabled by default. | |
1da177e4 | 67 | |
c63ca3c8 JJ |
68 | oldalloc This disables the Orlov block allocator and enables |
69 | the old block allocator. Orlov should have better | |
70 | performance - we'd like to get some feedback if it's | |
71 | the contrary for you. | |
1da177e4 | 72 | |
c63ca3c8 JJ |
73 | user_xattr Enables Extended User Attributes. Additionally, you |
74 | need to have extended attribute support enabled in the | |
75 | kernel configuration (CONFIG_EXT3_FS_XATTR). See the | |
76 | attr(5) manual page and http://acl.bestbits.at/ to | |
77 | learn more about extended attributes. | |
85b87242 AG |
78 | |
79 | nouser_xattr Disables Extended User Attributes. | |
80 | ||
c63ca3c8 JJ |
81 | acl Enables POSIX Access Control Lists support. |
82 | Additionally, you need to have ACL support enabled in | |
83 | the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL). | |
84 | See the acl(5) manual page and http://acl.bestbits.at/ | |
85 | for more information. | |
1da177e4 | 86 | |
c63ca3c8 JJ |
87 | noacl This option disables POSIX Access Control List |
88 | support. | |
1da177e4 LT |
89 | |
90 | reservation | |
91 | ||
92 | noreservation | |
93 | ||
1da177e4 LT |
94 | bsddf (*) Make 'df' act like BSD. |
95 | minixdf Make 'df' act like Minix. | |
96 | ||
97 | check=none Don't do extra checking of bitmaps on mount. | |
c63ca3c8 | 98 | nocheck |
1da177e4 LT |
99 | |
100 | debug Extra debugging information is sent to syslog. | |
101 | ||
e3375ac7 | 102 | errors=remount-ro Remount the filesystem read-only on an error. |
1da177e4 LT |
103 | errors=continue Keep going on a filesystem error. |
104 | errors=panic Panic and halt the machine if an error occurs. | |
e3375ac7 PM |
105 | (These mount options override the errors behavior |
106 | specified in the superblock, which can be | |
107 | configured using tune2fs.) | |
1da177e4 | 108 | |
0e4fb5e2 HK |
109 | data_err=ignore(*) Just print an error message if an error occurs |
110 | in a file data buffer in ordered mode. | |
111 | data_err=abort Abort the journal if an error occurs in a file | |
112 | data buffer in ordered mode. | |
113 | ||
1da177e4 | 114 | grpid Give objects the same group ID as their creator. |
c63ca3c8 | 115 | bsdgroups |
1da177e4 LT |
116 | |
117 | nogrpid (*) New objects have the group ID of their creator. | |
118 | sysvgroups | |
119 | ||
120 | resgid=n The group ID which may use the reserved blocks. | |
121 | ||
122 | resuid=n The user ID which may use the reserved blocks. | |
123 | ||
124 | sb=n Use alternate superblock at this location. | |
125 | ||
c63ca3c8 JJ |
126 | quota |
127 | noquota | |
1da177e4 LT |
128 | grpquota |
129 | usrquota | |
130 | ||
ade1a29e BP |
131 | bh (*) ext3 associates buffer heads to data pages to |
132 | nobh (a) cache disk block mapping information | |
133 | (b) link pages into transaction to provide | |
134 | ordering guarantees. | |
135 | "bh" option forces use of buffer heads. | |
136 | "nobh" option tries to avoid associating buffer | |
137 | heads (supported only for "writeback" mode). | |
138 | ||
1da177e4 LT |
139 | |
140 | Specification | |
141 | ============= | |
c63ca3c8 JJ |
142 | Ext3 shares all disk implementation with the ext2 filesystem, and adds |
143 | transactions capabilities to ext2. Journaling is done by the Journaling Block | |
144 | Device layer. | |
1da177e4 LT |
145 | |
146 | Journaling Block Device layer | |
147 | ----------------------------- | |
7356337b SZ |
148 | The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed |
149 | to add journaling capabilities to a block device. The ext3 filesystem code | |
150 | will inform the JBD of modifications it is performing (called a transaction). | |
151 | The journal supports the transactions start and stop, and in case of a crash, | |
152 | the journal can replay the transactions to quickly put the partition back into | |
153 | a consistent state. | |
1da177e4 | 154 | |
c63ca3c8 JJ |
155 | Handles represent a single atomic update to a filesystem. JBD can handle an |
156 | external journal on a block device. | |
1da177e4 LT |
157 | |
158 | Data Mode | |
159 | --------- | |
c63ca3c8 | 160 | There are 3 different data modes: |
1da177e4 LT |
161 | |
162 | * writeback mode | |
c63ca3c8 JJ |
163 | In data=writeback mode, ext3 does not journal data at all. This mode provides |
164 | a similar level of journaling as that of XFS, JFS, and ReiserFS in its default | |
165 | mode - metadata journaling. A crash+recovery can cause incorrect data to | |
166 | appear in files which were written shortly before the crash. This mode will | |
167 | typically provide the best ext3 performance. | |
1da177e4 LT |
168 | |
169 | * ordered mode | |
c63ca3c8 JJ |
170 | In data=ordered mode, ext3 only officially journals metadata, but it logically |
171 | groups metadata and data blocks into a single unit called a transaction. When | |
172 | it's time to write the new metadata out to disk, the associated data blocks | |
173 | are written first. In general, this mode performs slightly slower than | |
174 | writeback but significantly faster than journal mode. | |
1da177e4 LT |
175 | |
176 | * journal mode | |
c63ca3c8 JJ |
177 | data=journal mode provides full data and metadata journaling. All new data is |
178 | written to the journal first, and then to its final location. | |
179 | In the event of a crash, the journal can be replayed, bringing both data and | |
180 | metadata into a consistent state. This mode is the slowest except when data | |
181 | needs to be read from and written to disk at the same time where it | |
7356337b | 182 | outperforms all other modes. |
1da177e4 LT |
183 | |
184 | Compatibility | |
185 | ------------- | |
186 | ||
187 | Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. | |
c63ca3c8 JJ |
188 | Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as |
189 | Ext2. | |
190 | ||
1da177e4 LT |
191 | |
192 | External Tools | |
193 | ============== | |
c63ca3c8 JJ |
194 | See manual pages to learn more. |
195 | ||
196 | tune2fs: create a ext3 journal on a ext2 partition with the -j flag. | |
197 | mke2fs: create a ext3 partition with the -j flag. | |
198 | debugfs: ext2 and ext3 file system debugger. | |
e56d5ae3 | 199 | ext2online: online (mounted) ext2 and ext3 filesystem resizer |
1da177e4 | 200 | |
1da177e4 LT |
201 | |
202 | References | |
203 | ========== | |
204 | ||
c63ca3c8 JJ |
205 | kernel source: <file:fs/ext3/> |
206 | <file:fs/jbd/> | |
1da177e4 | 207 | |
c63ca3c8 | 208 | programs: http://e2fsprogs.sourceforge.net/ |
e56d5ae3 | 209 | http://ext2resize.sourceforge.net |
1da177e4 | 210 | |
ab03eca8 JM |
211 | useful links: http://www.ibm.com/developerworks/library/l-fs7.html |
212 | http://www.ibm.com/developerworks/library/l-fs8.html |