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Based on kernel version 2.6.33. Page generated on 2010-02-24 15:36 EST.

1	
2	Ext3 Filesystem
3	===============
4	
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,
7	Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.
8	
9	Ext3 is the ext2 filesystem enhanced with journalling capabilities.
10	
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_dev=devnum	When the external journal device's major/minor numbers
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.
34	
35	norecovery		Don't load the journal on mounting. Note that this forces
36	noload			mount of inconsistent filesystem, which can lead to
37				various problems.
38	
39	data=journal		All data are committed into the journal prior to being
40				written into the main file system.
41	
42	data=ordered	(*)	All data are forced directly out to the main file
43				system prior to its metadata being committed to the
44				journal.
45	
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.
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.
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).
59				Setting it to very large values will improve
60				performance.
61	
62	barrier=1		This enables/disables barriers.  barrier=0 disables
63				it, barrier=1 enables it.
64	
65	orlov		(*)	This enables the new Orlov block allocator. It is
66				enabled by default.
67	
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.
72	
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.
78	
79	nouser_xattr		Disables Extended User Attributes.
80	
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.
86	
87	noacl			This option disables POSIX Access Control List
88				support.
89	
90	reservation
91	
92	noreservation
93	
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.
98	nocheck
99	
100	debug			Extra debugging information is sent to syslog.
101	
102	errors=remount-ro	Remount the filesystem read-only on an error.
103	errors=continue		Keep going on a filesystem error.
104	errors=panic		Panic and halt the machine if an error occurs.
105				(These mount options override the errors behavior
106				specified in the superblock, which can be
107				configured using tune2fs.)
108	
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	
114	grpid			Give objects the same group ID as their creator.
115	bsdgroups
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	
126	quota			These options are ignored by the filesystem. They
127	noquota			are used only by quota tools to recognize volumes
128	grpquota		where quota should be turned on. See documentation
129	usrquota		in the quota-tools package for more details
130				(http://sourceforge.net/projects/linuxquota).
131	
132	jqfmt=<quota type>	These options tell filesystem details about quota
133	usrjquota=<file>	so that quota information can be properly updated
134	grpjquota=<file>	during journal replay. They replace the above
135				quota options. See documentation in the quota-tools
136				package for more details
137				(http://sourceforge.net/projects/linuxquota).
138	
139	bh		(*)	ext3 associates buffer heads to data pages to
140	nobh			(a) cache disk block mapping information
141				(b) link pages into transaction to provide
142				    ordering guarantees.
143				"bh" option forces use of buffer heads.
144				"nobh" option tries to avoid associating buffer
145				heads (supported only for "writeback" mode).
146	
147	
148	Specification
149	=============
150	Ext3 shares all disk implementation with the ext2 filesystem, and adds
151	transactions capabilities to ext2.  Journaling is done by the Journaling Block
152	Device layer.
153	
154	Journaling Block Device layer
155	-----------------------------
156	The Journaling Block Device layer (JBD) isn't ext3 specific.  It was designed
157	to add journaling capabilities to a block device.  The ext3 filesystem code
158	will inform the JBD of modifications it is performing (called a transaction).
159	The journal supports the transactions start and stop, and in case of a crash,
160	the journal can replay the transactions to quickly put the partition back into
161	a consistent state.
162	
163	Handles represent a single atomic update to a filesystem.  JBD can handle an
164	external journal on a block device.
165	
166	Data Mode
167	---------
168	There are 3 different data modes:
169	
170	* writeback mode
171	In data=writeback mode, ext3 does not journal data at all.  This mode provides
172	a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
173	mode - metadata journaling.  A crash+recovery can cause incorrect data to
174	appear in files which were written shortly before the crash.  This mode will
175	typically provide the best ext3 performance.
176	
177	* ordered mode
178	In data=ordered mode, ext3 only officially journals metadata, but it logically
179	groups metadata and data blocks into a single unit called a transaction.  When
180	it's time to write the new metadata out to disk, the associated data blocks
181	are written first.  In general, this mode performs slightly slower than
182	writeback but significantly faster than journal mode.
183	
184	* journal mode
185	data=journal mode provides full data and metadata journaling.  All new data is
186	written to the journal first, and then to its final location.
187	In the event of a crash, the journal can be replayed, bringing both data and
188	metadata into a consistent state.  This mode is the slowest except when data
189	needs to be read from and written to disk at the same time where it
190	outperforms all other modes.
191	
192	Compatibility
193	-------------
194	
195	Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.
196	Ext3 is fully compatible with Ext2.  Ext3 partitions can easily be mounted as
197	Ext2.
198	
199	
200	External Tools
201	==============
202	See manual pages to learn more.
203	
204	tune2fs: 	create a ext3 journal on a ext2 partition with the -j flag.
205	mke2fs: 	create a ext3 partition with the -j flag.
206	debugfs: 	ext2 and ext3 file system debugger.
207	ext2online:	online (mounted) ext2 and ext3 filesystem resizer
208	
209	
210	References
211	==========
212	
213	kernel source:	<file:fs/ext3/>
214			<file:fs/jbd/>
215	
216	programs: 	http://e2fsprogs.sourceforge.net/
217			http://ext2resize.sourceforge.net
218	
219	useful links:	http://www.ibm.com/developerworks/library/l-fs7.html
220			http://www.ibm.com/developerworks/library/l-fs8.html
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