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
=======
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
minixdf Make 'df' act like Minix.
check=none Don't do extra checking of bitmaps on mount.
-nocheck
+nocheck
debug Extra debugging information is sent to syslog.
errors=panic Panic and halt the machine if an error occurs.
grpid Give objects the same group ID as their creator.
-bsdgroups
+bsdgroups
nogrpid (*) New objects have the group ID of their creator.
sysvgroups
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/
projects / linux-2.6 / commitdiff