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Diffstat (limited to 'Documentation/filesystems/ext3.txt')
-rw-r--r-- | Documentation/filesystems/ext3.txt | 209 |
1 files changed, 3 insertions, 206 deletions
diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt index 7ed0d17d6721..58758fbef9e0 100644 --- a/Documentation/filesystems/ext3.txt +++ b/Documentation/filesystems/ext3.txt | |||
@@ -6,210 +6,7 @@ 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, | 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. | 7 | Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie. |
8 | 8 | ||
9 | Ext3 is the ext2 filesystem enhanced with journalling capabilities. | 9 | Ext3 is the ext2 filesystem enhanced with journalling capabilities. The |
10 | filesystem is a subset of ext4 filesystem so use ext4 driver for accessing | ||
11 | ext3 filesystems. | ||
10 | 12 | ||
11 | Options | ||
12 | ======= | ||
13 | |||
14 | When mounting an ext3 filesystem, the following option are accepted: | ||
15 | (*) == default | ||
16 | |||
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 | |||
22 | journal=update Update the ext3 file system's journal to the current | ||
23 | format. | ||
24 | |||
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. | ||
28 | |||
29 | journal_path=path | ||
30 | journal_dev=devnum When the external journal device's major/minor numbers | ||
31 | have changed, these options allow the user to specify | ||
32 | the new journal location. The journal device is | ||
33 | identified through either its new major/minor numbers | ||
34 | encoded in devnum, or via a path to the device. | ||
35 | |||
36 | norecovery Don't load the journal on mounting. Note that this forces | ||
37 | noload mount of inconsistent filesystem, which can lead to | ||
38 | various problems. | ||
39 | |||
40 | data=journal All data are committed into the journal prior to being | ||
41 | written into the main file system. | ||
42 | |||
43 | data=ordered (*) All data are forced directly out to the main file | ||
44 | system prior to its metadata being committed to the | ||
45 | journal. | ||
46 | |||
47 | data=writeback Data ordering is not preserved, data may be written | ||
48 | into the main file system after its metadata has been | ||
49 | committed to the journal. | ||
50 | |||
51 | commit=nrsec (*) Ext3 can be told to sync all its data and metadata | ||
52 | every 'nrsec' seconds. The default value is 5 seconds. | ||
53 | This means that if you lose your power, you will lose | ||
54 | as much as the latest 5 seconds of work (your | ||
55 | filesystem will not be damaged though, thanks to the | ||
56 | journaling). This default value (or any low value) | ||
57 | will hurt performance, but it's good for data-safety. | ||
58 | Setting it to 0 will have the same effect as leaving | ||
59 | it at the default (5 seconds). | ||
60 | Setting it to very large values will improve | ||
61 | performance. | ||
62 | |||
63 | barrier=<0|1(*)> This enables/disables the use of write barriers in | ||
64 | barrier (*) the jbd code. barrier=0 disables, barrier=1 enables. | ||
65 | nobarrier This also requires an IO stack which can support | ||
66 | barriers, and if jbd gets an error on a barrier | ||
67 | write, it will disable again with a warning. | ||
68 | Write barriers enforce proper on-disk ordering | ||
69 | of journal commits, making volatile disk write caches | ||
70 | safe to use, at some performance penalty. If | ||
71 | your disks are battery-backed in one way or another, | ||
72 | disabling barriers may safely improve performance. | ||
73 | The mount options "barrier" and "nobarrier" can | ||
74 | also be used to enable or disable barriers, for | ||
75 | consistency with other ext3 mount options. | ||
76 | |||
77 | user_xattr Enables Extended User Attributes. Additionally, you | ||
78 | need to have extended attribute support enabled in the | ||
79 | kernel configuration (CONFIG_EXT3_FS_XATTR). See the | ||
80 | attr(5) manual page and http://acl.bestbits.at/ to | ||
81 | learn more about extended attributes. | ||
82 | |||
83 | nouser_xattr Disables Extended User Attributes. | ||
84 | |||
85 | acl Enables POSIX Access Control Lists support. | ||
86 | Additionally, you need to have ACL support enabled in | ||
87 | the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL). | ||
88 | See the acl(5) manual page and http://acl.bestbits.at/ | ||
89 | for more information. | ||
90 | |||
91 | noacl This option disables POSIX Access Control List | ||
92 | support. | ||
93 | |||
94 | reservation | ||
95 | |||
96 | noreservation | ||
97 | |||
98 | bsddf (*) Make 'df' act like BSD. | ||
99 | minixdf Make 'df' act like Minix. | ||
100 | |||
101 | check=none Don't do extra checking of bitmaps on mount. | ||
102 | nocheck | ||
103 | |||
104 | debug Extra debugging information is sent to syslog. | ||
105 | |||
106 | errors=remount-ro Remount the filesystem read-only on an error. | ||
107 | errors=continue Keep going on a filesystem error. | ||
108 | errors=panic Panic and halt the machine if an error occurs. | ||
109 | (These mount options override the errors behavior | ||
110 | specified in the superblock, which can be | ||
111 | configured using tune2fs.) | ||
112 | |||
113 | data_err=ignore(*) Just print an error message if an error occurs | ||
114 | in a file data buffer in ordered mode. | ||
115 | data_err=abort Abort the journal if an error occurs in a file | ||
116 | data buffer in ordered mode. | ||
117 | |||
118 | grpid Give objects the same group ID as their creator. | ||
119 | bsdgroups | ||
120 | |||
121 | nogrpid (*) New objects have the group ID of their creator. | ||
122 | sysvgroups | ||
123 | |||
124 | resgid=n The group ID which may use the reserved blocks. | ||
125 | |||
126 | resuid=n The user ID which may use the reserved blocks. | ||
127 | |||
128 | sb=n Use alternate superblock at this location. | ||
129 | |||
130 | quota These options are ignored by the filesystem. They | ||
131 | noquota are used only by quota tools to recognize volumes | ||
132 | grpquota where quota should be turned on. See documentation | ||
133 | usrquota in the quota-tools package for more details | ||
134 | (http://sourceforge.net/projects/linuxquota). | ||
135 | |||
136 | jqfmt=<quota type> These options tell filesystem details about quota | ||
137 | usrjquota=<file> so that quota information can be properly updated | ||
138 | grpjquota=<file> during journal replay. They replace the above | ||
139 | quota options. See documentation in the quota-tools | ||
140 | package for more details | ||
141 | (http://sourceforge.net/projects/linuxquota). | ||
142 | |||
143 | Specification | ||
144 | ============= | ||
145 | Ext3 shares all disk implementation with the ext2 filesystem, and adds | ||
146 | transactions capabilities to ext2. Journaling is done by the Journaling Block | ||
147 | Device layer. | ||
148 | |||
149 | Journaling Block Device layer | ||
150 | ----------------------------- | ||
151 | The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed | ||
152 | to add journaling capabilities to a block device. The ext3 filesystem code | ||
153 | will inform the JBD of modifications it is performing (called a transaction). | ||
154 | The journal supports the transactions start and stop, and in case of a crash, | ||
155 | the journal can replay the transactions to quickly put the partition back into | ||
156 | a consistent state. | ||
157 | |||
158 | Handles represent a single atomic update to a filesystem. JBD can handle an | ||
159 | external journal on a block device. | ||
160 | |||
161 | Data Mode | ||
162 | --------- | ||
163 | There are 3 different data modes: | ||
164 | |||
165 | * writeback mode | ||
166 | In data=writeback mode, ext3 does not journal data at all. This mode provides | ||
167 | a similar level of journaling as that of XFS, JFS, and ReiserFS in its default | ||
168 | mode - metadata journaling. A crash+recovery can cause incorrect data to | ||
169 | appear in files which were written shortly before the crash. This mode will | ||
170 | typically provide the best ext3 performance. | ||
171 | |||
172 | * ordered mode | ||
173 | In data=ordered mode, ext3 only officially journals metadata, but it logically | ||
174 | groups metadata and data blocks into a single unit called a transaction. When | ||
175 | it's time to write the new metadata out to disk, the associated data blocks | ||
176 | are written first. In general, this mode performs slightly slower than | ||
177 | writeback but significantly faster than journal mode. | ||
178 | |||
179 | * journal mode | ||
180 | data=journal mode provides full data and metadata journaling. All new data is | ||
181 | written to the journal first, and then to its final location. | ||
182 | In the event of a crash, the journal can be replayed, bringing both data and | ||
183 | metadata into a consistent state. This mode is the slowest except when data | ||
184 | needs to be read from and written to disk at the same time where it | ||
185 | outperforms all other modes. | ||
186 | |||
187 | Compatibility | ||
188 | ------------- | ||
189 | |||
190 | Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. | ||
191 | Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as | ||
192 | Ext2. | ||
193 | |||
194 | |||
195 | External Tools | ||
196 | ============== | ||
197 | See manual pages to learn more. | ||
198 | |||
199 | tune2fs: create a ext3 journal on a ext2 partition with the -j flag. | ||
200 | mke2fs: create a ext3 partition with the -j flag. | ||
201 | debugfs: ext2 and ext3 file system debugger. | ||
202 | ext2online: online (mounted) ext2 and ext3 filesystem resizer | ||
203 | |||
204 | |||
205 | References | ||
206 | ========== | ||
207 | |||
208 | kernel source: <file:fs/ext3/> | ||
209 | <file:fs/jbd/> | ||
210 | |||
211 | programs: http://e2fsprogs.sourceforge.net/ | ||
212 | http://ext2resize.sourceforge.net | ||
213 | |||
214 | useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html | ||
215 | http://www.ibm.com/developerworks/library/l-fs8/index.html | ||