Based on kernel version 2.6.26. Page generated on 2008-07-16 21:12 EST.
1 2 Ext3 Filesystem 3 =============== 4 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, 7 Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie. 8 9 Ext3 is the ext2 filesystem enhanced with journalling capabilities. 10 11 Options 12 ======= 13 14 When mounting an ext3 filesystem, the following option are accepted: 15 (*) == default 16 17 journal=update Update the ext3 file system's journal to the current 18 format. 19 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. 23 24 journal_dev=devnum When the external journal device's major/minor numbers 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. 29 30 noload Don't load the journal on mounting. 31 32 data=journal All data are committed into the journal prior to being 33 written into the main file system. 34 35 data=ordered (*) All data are forced directly out to the main file 36 system prior to its metadata being committed to the 37 journal. 38 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. 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. 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). 52 Setting it to very large values will improve 53 performance. 54 55 barrier=1 This enables/disables barriers. barrier=0 disables 56 it, barrier=1 enables it. 57 58 orlov (*) This enables the new Orlov block allocator. It is 59 enabled by default. 60 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. 65 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. 71 72 nouser_xattr Disables Extended User Attributes. 73 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. 79 80 noacl This option disables POSIX Access Control List 81 support. 82 83 reservation 84 85 noreservation 86 87 bsddf (*) Make 'df' act like BSD. 88 minixdf Make 'df' act like Minix. 89 90 check=none Don't do extra checking of bitmaps on mount. 91 nocheck 92 93 debug Extra debugging information is sent to syslog. 94 95 errors=remount-ro(*) Remount the filesystem read-only on an error. 96 errors=continue Keep going on a filesystem error. 97 errors=panic Panic and halt the machine if an error occurs. 98 99 grpid Give objects the same group ID as their creator. 100 bsdgroups 101 102 nogrpid (*) New objects have the group ID of their creator. 103 sysvgroups 104 105 resgid=n The group ID which may use the reserved blocks. 106 107 resuid=n The user ID which may use the reserved blocks. 108 109 sb=n Use alternate superblock at this location. 110 111 quota 112 noquota 113 grpquota 114 usrquota 115 116 bh (*) ext3 associates buffer heads to data pages to 117 nobh (a) cache disk block mapping information 118 (b) link pages into transaction to provide 119 ordering guarantees. 120 "bh" option forces use of buffer heads. 121 "nobh" option tries to avoid associating buffer 122 heads (supported only for "writeback" mode). 123 124 125 Specification 126 ============= 127 Ext3 shares all disk implementation with the ext2 filesystem, and adds 128 transactions capabilities to ext2. Journaling is done by the Journaling Block 129 Device layer. 130 131 Journaling Block Device layer 132 ----------------------------- 133 The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed 134 to add journaling capabilities to a block device. The ext3 filesystem code 135 will inform the JBD of modifications it is performing (called a transaction). 136 The journal supports the transactions start and stop, and in case of a crash, 137 the journal can replay the transactions to quickly put the partition back into 138 a consistent state. 139 140 Handles represent a single atomic update to a filesystem. JBD can handle an 141 external journal on a block device. 142 143 Data Mode 144 --------- 145 There are 3 different data modes: 146 147 * writeback mode 148 In data=writeback mode, ext3 does not journal data at all. This mode provides 149 a similar level of journaling as that of XFS, JFS, and ReiserFS in its default 150 mode - metadata journaling. A crash+recovery can cause incorrect data to 151 appear in files which were written shortly before the crash. This mode will 152 typically provide the best ext3 performance. 153 154 * ordered mode 155 In data=ordered mode, ext3 only officially journals metadata, but it logically 156 groups metadata and data blocks into a single unit called a transaction. When 157 it's time to write the new metadata out to disk, the associated data blocks 158 are written first. In general, this mode performs slightly slower than 159 writeback but significantly faster than journal mode. 160 161 * journal mode 162 data=journal mode provides full data and metadata journaling. All new data is 163 written to the journal first, and then to its final location. 164 In the event of a crash, the journal can be replayed, bringing both data and 165 metadata into a consistent state. This mode is the slowest except when data 166 needs to be read from and written to disk at the same time where it 167 outperforms all other modes. 168 169 Compatibility 170 ------------- 171 172 Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. 173 Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as 174 Ext2. 175 176 177 External Tools 178 ============== 179 See manual pages to learn more. 180 181 tune2fs: create a ext3 journal on a ext2 partition with the -j flag. 182 mke2fs: create a ext3 partition with the -j flag. 183 debugfs: ext2 and ext3 file system debugger. 184 ext2online: online (mounted) ext2 and ext3 filesystem resizer 185 186 187 References 188 ========== 189 190 kernel source: <file:fs/ext3/> 191 <file:fs/jbd/> 192 193 programs: http://e2fsprogs.sourceforge.net/ 194 http://ext2resize.sourceforge.net 195 196 useful links: http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html 197 http://www-106.ibm.com/developerworks/linux/library/l-fs7/ 198 http://www-106.ibm.com/developerworks/linux/library/l-fs8/