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diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt index 9ab7f446f7a..7ed0d17d672 100644 --- a/Documentation/filesystems/ext3.txt +++ b/Documentation/filesystems/ext3.txt @@ -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 ======= @@ -14,85 +14,109 @@ 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. +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=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=update Update the ext3 file system's journal to the current + format. -noload Don't load the journal on mounting. +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. -data=journal All data are committed into the journal prior - to being written into the main file system. +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. + 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. - -orlov (*) This enables the new Orlov block allocator. It's 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. - -user_xattr (*) Enables POSIX Extended Attributes. It's enabled by - default, however you need to confifure its support - (CONFIG_EXT3_FS_XATTR). This is neccesary if you want - to use POSIX Acces Control Lists support. You can visit - http://acl.bestbits.at to know more about POSIX Extended - attributes. - -nouser_xattr Disables POSIX Extended Attributes. - -acl (*) Enables POSIX Access Control Lists support. This is - enabled by default, however you need to configure - its support (CONFIG_EXT3_FS_POSIX_ACL). If you want - to know more about ACLs visit http://acl.bestbits.at - -noacl This option disables POSIX Access Control List support. +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 -resize= - bsddf (*) Make 'df' act like BSD. 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=remount-ro(*) Remount the filesystem read-only on an error. +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 +bsdgroups nogrpid (*) New objects have the group ID of their creator. sysvgroups @@ -103,81 +127,89 @@ 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) -grpquota -usrquota +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 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 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 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 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. +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. +ext2online: online (mounted) ext2 and ext3 filesystem resizer -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/ + http://ext2resize.sourceforge.net -useful link: - 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/ +useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html + http://www.ibm.com/developerworks/library/l-fs8/index.html |