Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | |
| 2 | Ext3 Filesystem |
| 3 | =============== |
| 4 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 5 | Ext3 was originally released in September 1999. Written by Stephen Tweedie |
| 6 | for the 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 7 | Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie. |
| 8 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 9 | Ext3 is the ext2 filesystem enhanced with journalling capabilities. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 10 | |
| 11 | Options |
| 12 | ======= |
| 13 | |
| 14 | When mounting an ext3 filesystem, the following option are accepted: |
| 15 | (*) == default |
| 16 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 17 | journal=update Update the ext3 file system's journal to the current |
| 18 | format. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 19 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 20 | journal=inum When a journal already exists, this option is ignored. |
| 21 | Otherwise, it specifies the number of the inode which |
| 22 | will represent the ext3 file system's journal file. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 23 | |
Johann Lombardi | 71b9625 | 2006-01-08 01:03:20 -0800 | [diff] [blame] | 24 | journal_dev=devnum When the external journal device's major/minor numbers |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 25 | have changed, this option allows the user to specify |
| 26 | the new journal location. The journal device is |
| 27 | identified through its new major/minor numbers encoded |
| 28 | in devnum. |
Johann Lombardi | 71b9625 | 2006-01-08 01:03:20 -0800 | [diff] [blame] | 29 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 30 | noload Don't load the journal on mounting. |
| 31 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 32 | data=journal All data are committed into the journal prior to being |
| 33 | written into the main file system. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 34 | |
| 35 | data=ordered (*) All data are forced directly out to the main file |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 36 | system prior to its metadata being committed to the |
| 37 | journal. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 38 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 39 | data=writeback Data ordering is not preserved, data may be written |
| 40 | into the main file system after its metadata has been |
| 41 | committed to the journal. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 42 | |
| 43 | commit=nrsec (*) Ext3 can be told to sync all its data and metadata |
| 44 | every 'nrsec' seconds. The default value is 5 seconds. |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 45 | This means that if you lose your power, you will lose |
| 46 | as much as the latest 5 seconds of work (your |
| 47 | filesystem will not be damaged though, thanks to the |
| 48 | journaling). This default value (or any low value) |
| 49 | will hurt performance, but it's good for data-safety. |
| 50 | Setting it to 0 will have the same effect as leaving |
| 51 | it at the default (5 seconds). |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 52 | Setting it to very large values will improve |
| 53 | performance. |
| 54 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 55 | barrier=1 This enables/disables barriers. barrier=0 disables |
| 56 | it, barrier=1 enables it. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 57 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 58 | orlov (*) This enables the new Orlov block allocator. It is |
| 59 | enabled by default. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 60 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 61 | oldalloc This disables the Orlov block allocator and enables |
| 62 | the old block allocator. Orlov should have better |
| 63 | performance - we'd like to get some feedback if it's |
| 64 | the contrary for you. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 65 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 66 | user_xattr Enables Extended User Attributes. Additionally, you |
| 67 | need to have extended attribute support enabled in the |
| 68 | kernel configuration (CONFIG_EXT3_FS_XATTR). See the |
| 69 | attr(5) manual page and http://acl.bestbits.at/ to |
| 70 | learn more about extended attributes. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 71 | |
Andreas Gruenbacher | 85b8724 | 2005-12-12 00:37:04 -0800 | [diff] [blame] | 72 | nouser_xattr Disables Extended User Attributes. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 73 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 74 | acl Enables POSIX Access Control Lists support. |
| 75 | Additionally, you need to have ACL support enabled in |
| 76 | the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL). |
| 77 | See the acl(5) manual page and http://acl.bestbits.at/ |
| 78 | for more information. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 79 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 80 | noacl This option disables POSIX Access Control List |
| 81 | support. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 82 | |
| 83 | reservation |
| 84 | |
| 85 | noreservation |
| 86 | |
| 87 | resize= |
| 88 | |
| 89 | bsddf (*) Make 'df' act like BSD. |
| 90 | minixdf Make 'df' act like Minix. |
| 91 | |
| 92 | check=none Don't do extra checking of bitmaps on mount. |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 93 | nocheck |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 94 | |
| 95 | debug Extra debugging information is sent to syslog. |
| 96 | |
| 97 | errors=remount-ro(*) Remount the filesystem read-only on an error. |
| 98 | errors=continue Keep going on a filesystem error. |
| 99 | errors=panic Panic and halt the machine if an error occurs. |
| 100 | |
| 101 | grpid Give objects the same group ID as their creator. |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 102 | bsdgroups |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 103 | |
| 104 | nogrpid (*) New objects have the group ID of their creator. |
| 105 | sysvgroups |
| 106 | |
| 107 | resgid=n The group ID which may use the reserved blocks. |
| 108 | |
| 109 | resuid=n The user ID which may use the reserved blocks. |
| 110 | |
| 111 | sb=n Use alternate superblock at this location. |
| 112 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 113 | quota |
| 114 | noquota |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 115 | grpquota |
| 116 | usrquota |
| 117 | |
| 118 | |
| 119 | Specification |
| 120 | ============= |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 121 | Ext3 shares all disk implementation with the ext2 filesystem, and adds |
| 122 | transactions capabilities to ext2. Journaling is done by the Journaling Block |
| 123 | Device layer. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 124 | |
| 125 | Journaling Block Device layer |
| 126 | ----------------------------- |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 127 | The Journaling Block Device layer (JBD) isn't ext3 specific. It was design to |
| 128 | add journaling capabilities on a block device. The ext3 filesystem code will |
| 129 | inform the JBD of modifications it is performing (called a transaction). The |
| 130 | journal supports the transactions start and stop, and in case of crash, the |
| 131 | journal can replayed the transactions to put the partition back in a |
| 132 | consistent state fast. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 133 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 134 | Handles represent a single atomic update to a filesystem. JBD can handle an |
| 135 | external journal on a block device. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 136 | |
| 137 | Data Mode |
| 138 | --------- |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 139 | There are 3 different data modes: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 140 | |
| 141 | * writeback mode |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 142 | In data=writeback mode, ext3 does not journal data at all. This mode provides |
| 143 | a similar level of journaling as that of XFS, JFS, and ReiserFS in its default |
| 144 | mode - metadata journaling. A crash+recovery can cause incorrect data to |
| 145 | appear in files which were written shortly before the crash. This mode will |
| 146 | typically provide the best ext3 performance. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 147 | |
| 148 | * ordered mode |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 149 | In data=ordered mode, ext3 only officially journals metadata, but it logically |
| 150 | groups metadata and data blocks into a single unit called a transaction. When |
| 151 | it's time to write the new metadata out to disk, the associated data blocks |
| 152 | are written first. In general, this mode performs slightly slower than |
| 153 | writeback but significantly faster than journal mode. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 154 | |
| 155 | * journal mode |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 156 | data=journal mode provides full data and metadata journaling. All new data is |
| 157 | written to the journal first, and then to its final location. |
| 158 | In the event of a crash, the journal can be replayed, bringing both data and |
| 159 | metadata into a consistent state. This mode is the slowest except when data |
| 160 | needs to be read from and written to disk at the same time where it |
| 161 | outperforms all others modes. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 162 | |
| 163 | Compatibility |
| 164 | ------------- |
| 165 | |
| 166 | Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 167 | Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as |
| 168 | Ext2. |
| 169 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 170 | |
| 171 | External Tools |
| 172 | ============== |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 173 | See manual pages to learn more. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 174 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 175 | tune2fs: create a ext3 journal on a ext2 partition with the -j flag. |
| 176 | mke2fs: create a ext3 partition with the -j flag. |
| 177 | debugfs: ext2 and ext3 file system debugger. |
| 178 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 179 | |
| 180 | References |
| 181 | ========== |
| 182 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 183 | kernel source: <file:fs/ext3/> |
| 184 | <file:fs/jbd/> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 185 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 186 | programs: http://e2fsprogs.sourceforge.net/ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 187 | |
Jesper Juhl | c63ca3c | 2006-01-09 20:53:57 -0800 | [diff] [blame] | 188 | useful links: http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 189 | http://www-106.ibm.com/developerworks/linux/library/l-fs7/ |
| 190 | http://www-106.ibm.com/developerworks/linux/library/l-fs8/ |