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Diffstat (limited to 'Documentation/filesystems/ext3.txt')
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diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt index 7ed0d17d6721..58758fbef9e0 100644 --- a/Documentation/filesystems/ext3.txt +++ b/Documentation/filesystems/ext3.txt @@ -6,210 +6,7 @@ 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. +Ext3 is the ext2 filesystem enhanced with journalling capabilities. The +filesystem is a subset of ext4 filesystem so use ext4 driver for accessing +ext3 filesystems. -Options -======= - -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_path=path -journal_dev=devnum When the external journal device's major/minor numbers - have changed, these options allow the user to specify - the new journal location. The journal device is - identified through either its new major/minor numbers - encoded in devnum, or via a path to the device. - -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. - -reservation - -noreservation - -bsddf (*) Make 'df' act like BSD. -minixdf Make 'df' act like Minix. - -check=none Don't do extra checking of bitmaps on mount. -nocheck - -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. -bsdgroups - -nogrpid (*) New objects have the group ID of their creator. -sysvgroups - -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). - -Specification -============= -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. - -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. - - -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 - - -References -========== - -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 |