@@ -6,210 +6,7 @@ Ext3 was originally released in September 1999. Written by Stephen Tweedie
66for the 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger,
77Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.
88
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.
1012
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
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