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Commit c63ca3c8 authored by Jesper Juhl's avatar Jesper Juhl Committed by Linus Torvalds
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[PATCH] Docs update: small spelling, formating etc fixes for filesystems/ext3.txt 



Spelling fixes, formating changes and corrections for
 Documentation/filesystems/ext3.txt

Signed-off-by: default avatarJesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent c594a50d

Documentation/filesystems/ext3.txt

+90 −88
Original line number Diff line number Diff line
@@ -2,11 +2,11 @@ 
Ext3 Filesystem

===============



ext3 was originally released in September 1999. Written by Stephen Tweedie

for 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger, 

Ext3 was originally released in September 1999. Written by Stephen Tweedie

for the 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger,

Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie.



ext3 is ext2 filesystem enhanced with journalling capabilities. 

Ext3 is the ext2 filesystem enhanced with journalling capabilities.



Options

=======
@@ -14,69 +14,71 @@ Options 
When mounting an ext3 filesystem, the following option are accepted:

(*) == default



jounal=update		Update the ext3 file system's journal to the 

			current format.

journal=update		Update the ext3 file system's journal to the current

			format.



journal=inum		When a journal already exists, this option is 

			ignored. Otherwise, it specifies the number of

			the inode which will represent the ext3 file

			system's journal file.

journal=inum		When a journal already exists, this option is ignored.

			Otherwise, it specifies the number of the inode which

			will represent the ext3 file system's journal file.



journal_dev=devnum	When the external journal device's major/minor numbers

			have changed, this option allows to specify the new

			journal location. The journal device is identified

			through its new major/minor numbers encoded in devnum.

			have changed, this option allows the user to specify

			the new journal location.  The journal device is

			identified through its new major/minor numbers encoded

			in devnum.



noload			Don't load the journal on mounting.



data=journal		All data are committed into the journal prior

			to being written into the main file system.

data=journal		All data are committed into the journal prior to being

			written into the main file system.



data=ordered	(*)	All data are forced directly out to the main file

			system prior to its metadata being committed to

			the journal.

			system prior to its metadata being committed to the

			journal.



data=writeback		Data ordering is not preserved, data may be

			written into the main file system after its

			metadata has been committed to the journal.

data=writeback		Data ordering is not preserved, data may be written

			into the main file system after its metadata has been

			committed to the journal.



commit=nrsec	(*)	Ext3 can be told to sync all its data and metadata

			every 'nrsec' seconds. The default value is 5 seconds.

			This means that if you lose your power, you will lose,

			as much, the latest 5 seconds of work (your filesystem

			will not be damaged though, thanks to journaling). This

			default value (or any low value) will hurt performance,

			but it's good for data-safety. Setting it to 0 will

			have the same effect than leaving the default 5 sec.

			This means that if you lose your power, you will lose

			as much as the latest 5 seconds of work (your

			filesystem will not be damaged though, thanks to the

			journaling).  This default value (or any low value)

			will hurt performance, but it's good for data-safety.

			Setting it to 0 will have the same effect as leaving

			it at the default (5 seconds).

			Setting it to very large values will improve

			performance.



barrier=1		This enables/disables barriers. barrier=0 disables it,

			barrier=1 enables it.

barrier=1		This enables/disables barriers.  barrier=0 disables

			it, barrier=1 enables it.



orlov		(*)	This enables the new Orlov block allocator. It's enabled

			by default.

orlov		(*)	This enables the new Orlov block allocator. It is

			enabled by default.



oldalloc		This disables the Orlov block allocator and enables the

			old block allocator. Orlov should have better performance,

			we'd like to get some feedback if it's the contrary for

			you.

oldalloc		This disables the Orlov block allocator and enables

			the old block allocator.  Orlov should have better

			performance - we'd like to get some feedback if it's

			the contrary for you.



user_xattr		Enables Extended User Attributes. Additionally, you need

			to have extended attribute support enabled in the kernel

			configuration (CONFIG_EXT3_FS_XATTR). See the attr(5)

			manual page and http://acl.bestbits.at to learn more

			about extended attributes.

user_xattr		Enables Extended User Attributes.  Additionally, you

			need to have extended attribute support enabled in the

			kernel configuration (CONFIG_EXT3_FS_XATTR).  See the

			attr(5) manual page and http://acl.bestbits.at/ to

			learn more about extended attributes.



nouser_xattr		Disables Extended User Attributes.



acl			Enables POSIX Access Control Lists support.  Additionally,

			you need to have ACL support enabled in the kernel

			configuration (CONFIG_EXT3_FS_POSIX_ACL). See the acl(5)

			manual page and http://acl.bestbits.at for more

			information.

acl			Enables POSIX Access Control Lists support.

			Additionally, you need to have ACL support enabled in

			the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL).

			See the acl(5) manual page and http://acl.bestbits.at/

			for more information.



noacl			This option disables POSIX Access Control List support.

noacl			This option disables POSIX Access Control List

			support.



reservation
@@ -108,81 +110,81 @@ resuid=n The user ID which may use the reserved blocks. 


sb=n			Use alternate superblock at this location.



quota			Quota options are currently silently ignored.

noquota			(see fs/ext3/super.c, line 594)

quota

noquota

grpquota

usrquota





Specification

=============

ext3 shares all disk implementation with ext2 filesystem, and add

transactions capabilities to ext2.  Journaling is done by the

Journaling block device layer.

Ext3 shares all disk implementation with the ext2 filesystem, and adds

transactions capabilities to ext2.  Journaling is done by the Journaling Block

Device layer.



Journaling Block Device layer

-----------------------------

The Journaling Block Device layer (JBD) isn't ext3 specific.  It was

design to add journaling capabilities on a block device.  The ext3

filesystem code will inform the JBD of modifications it is performing

(Call a transaction).  the journal support the transactions start and

stop, and in case of crash, the journal can replayed the transactions

to put the partition on a consistent state fastly.

The Journaling Block Device layer (JBD) isn't ext3 specific.  It was design to

add journaling capabilities on a block device.  The ext3 filesystem code will

inform the JBD of modifications it is performing (called a transaction).  The

journal supports the transactions start and stop, and in case of crash, the

journal can replayed the transactions to put the partition back in a

consistent state fast.



handles represent a single atomic update to a filesystem.  JBD can

handle external journal on a block device.

Handles represent a single atomic update to a filesystem.  JBD can handle an

external journal on a block device.



Data Mode

---------

There's 3 different data modes:

There are 3 different data modes:



* writeback mode

In data=writeback mode, ext3 does not journal data at all.  This mode

provides a similar level of journaling as XFS, JFS, and ReiserFS in its

default mode - metadata journaling.  A crash+recovery can cause

incorrect data to appear in files which were written shortly before the

crash.  This mode will typically provide the best ext3 performance.

In data=writeback mode, ext3 does not journal data at all.  This mode provides

a similar level of journaling as that of XFS, JFS, and ReiserFS in its default

mode - metadata journaling.  A crash+recovery can cause incorrect data to

appear in files which were written shortly before the crash.  This mode will

typically provide the best ext3 performance.



* ordered mode

In data=ordered mode, ext3 only officially journals metadata, but it

logically groups metadata and data blocks into a single unit called a

transaction.  When it's time to write the new metadata out to disk, the

associated data blocks are written first.  In general, this mode

perform slightly slower than writeback but significantly faster than

journal mode.

In data=ordered mode, ext3 only officially journals metadata, but it logically

groups metadata and data blocks into a single unit called a transaction.  When

it's time to write the new metadata out to disk, the associated data blocks

are written first.  In general, this mode performs slightly slower than

writeback but significantly faster than journal mode.



* journal mode

data=journal mode provides full data and metadata journaling.  All new

data is written to the journal first, and then to its final location. 

In the event of a crash, the journal can be replayed, bringing both

data and metadata into a consistent state.  This mode is the slowest

except when data needs to be read from and written to disk at the same

time where it outperform all others mode.

data=journal mode provides full data and metadata journaling.  All new data is

written to the journal first, and then to its final location.

In the event of a crash, the journal can be replayed, bringing both data and

metadata into a consistent state.  This mode is the slowest except when data

needs to be read from and written to disk at the same time where it

outperforms all others modes.



Compatibility

-------------



Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`.

Ext3 is fully compatible with Ext2.  Ext3 partitions can easily be

mounted as Ext2.

Ext3 is fully compatible with Ext2.  Ext3 partitions can easily be mounted as

Ext2.





External Tools

==============

see manual pages to know more.

See manual pages to learn more.



tune2fs: 	create a ext3 journal on a ext2 partition with the -j flag.

mke2fs: 	create a ext3 partition with the -j flag.

debugfs: 	ext2 and ext3 file system debugger.



tune2fs: 	create a ext3 journal on a ext2 partition with the -j flags

mke2fs: 	create a ext3 partition with the -j flags

debugfs: 	ext2 and ext3 file system debugger



References

==========



kernel source:	file:/usr/src/linux/fs/ext3

		file:/usr/src/linux/fs/jbd

kernel source:	<file:fs/ext3/>

		<file:fs/jbd/>



programs: 	http://e2fsprogs.sourceforge.net

programs: 	http://e2fsprogs.sourceforge.net/



useful link:

		http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html

useful links:	http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html

		http://www-106.ibm.com/developerworks/linux/library/l-fs7/

		http://www-106.ibm.com/developerworks/linux/library/l-fs8/