path: root/Documentation/filesystems/ext3.txt
diff options
Diffstat (limited to 'Documentation/filesystems/ext3.txt')
1 files changed, 214 insertions, 0 deletions
diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt
new file mode 100644
index 00000000..293855e9
--- /dev/null
+++ b/Documentation/filesystems/ext3.txt
@@ -0,0 +1,214 @@
+Ext3 Filesystem
+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 the ext2 filesystem enhanced with journalling capabilities.
+When mounting an ext3 filesystem, the following option are accepted:
+(*) == default
+ro Mount filesystem read only. Note that ext3 will replay
+ the journal (and thus write to the partition) even when
+ mounted "read only". Mount options "ro,noload" can be
+ used to prevent writes to the filesystem.
+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_dev=devnum When the external journal device's major/minor numbers
+ 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.
+norecovery Don't load the journal on mounting. Note that this forces
+noload mount of inconsistent filesystem, which can lead to
+ various problems.
+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.
+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 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=<0|1(*)> This enables/disables the use of write barriers in
+barrier (*) the jbd code. barrier=0 disables, barrier=1 enables.
+nobarrier This also requires an IO stack which can support
+ barriers, and if jbd gets an error on a barrier
+ write, it will disable again with a warning.
+ Write barriers enforce proper on-disk ordering
+ of journal commits, making volatile disk write caches
+ safe to use, at some performance penalty. If
+ your disks are battery-backed in one way or another,
+ disabling barriers may safely improve performance.
+ The mount options "barrier" and "nobarrier" can
+ also be used to enable or disable barriers, for
+ consistency with other ext3 mount options.
+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.
+noacl This option disables POSIX Access Control List
+ support.
+bsddf (*) Make 'df' act like BSD.
+minixdf Make 'df' act like Minix.
+check=none Don't do extra checking of bitmaps on mount.
+debug Extra debugging information is sent to syslog.
+errors=remount-ro Remount the filesystem read-only on an error.
+errors=continue Keep going on a filesystem error.
+errors=panic Panic and halt the machine if an error occurs.
+ (These mount options override the errors behavior
+ specified in the superblock, which can be
+ configured using tune2fs.)
+data_err=ignore(*) Just print an error message if an error occurs
+ in a file data buffer in ordered mode.
+data_err=abort Abort the journal if an error occurs in a file
+ data buffer in ordered mode.
+grpid Give objects the same group ID as their creator.
+nogrpid (*) New objects have the group ID of their creator.
+resgid=n The group ID which may use the reserved blocks.
+resuid=n The user ID which may use the reserved blocks.
+sb=n Use alternate superblock at this location.
+quota These options are ignored by the filesystem. They
+noquota are used only by quota tools to recognize volumes
+grpquota where quota should be turned on. See documentation
+usrquota in the quota-tools package for more details
+ (http://sourceforge.net/projects/linuxquota).
+jqfmt=<quota type> These options tell filesystem details about quota
+usrjquota=<file> so that quota information can be properly updated
+grpjquota=<file> during journal replay. They replace the above
+ quota options. See documentation in the quota-tools
+ package for more details
+ (http://sourceforge.net/projects/linuxquota).
+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 designed
+to add journaling capabilities to 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 a crash,
+the journal can replay the transactions to quickly put the partition back into
+a consistent state.
+Handles represent a single atomic update to a filesystem. JBD can handle an
+external journal on a block device.
+Data Mode
+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 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 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
+outperforms all other modes.
+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
+External Tools
+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.
+ext2online: online (mounted) ext2 and ext3 filesystem resizer
+kernel source: <file:fs/ext3/>
+ <file:fs/jbd/>
+programs: http://e2fsprogs.sourceforge.net/
+ http://ext2resize.sourceforge.net
+useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html
+ http://www.ibm.com/developerworks/library/l-fs8/index.html