--- zzzz-none-000/linux-3.10.107/Documentation/filesystems/ext3.txt 2017-06-27 09:49:32.000000000 +0000 +++ scorpion-7490-727/linux-3.10.107/Documentation/filesystems/ext3.txt 2021-02-04 17:41:59.000000000 +0000 @@ -6,209 +6,7 @@ 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_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. - -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= These options tell filesystem details about quota -usrjquota= so that quota information can be properly updated -grpjquota= 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 `. -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: - - -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