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diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt new file mode 100644 index 0000000..9ab7f44 --- /dev/null +++ b/Documentation/filesystems/ext3.txt @@ -0,0 +1,183 @@ + +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, +Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie. + +ext3 is 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=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. + +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=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, 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. + 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. + +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 + +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. + +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 Quota options are currently silently ignored. +noquota (see fs/ext3/super.c, line 594) +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. + +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. + +handles represent a single atomic update to a filesystem. JBD can +handle external journal on a block device. + +Data Mode +--------- +There's 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. + +* 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. + +* 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. + +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 know more. + +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 + +programs: http://e2fsprogs.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/ |
