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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 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_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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