Based on kernel version 3.16. Page generated on 2014-08-06 21:39 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 ro Mount filesystem read only. Note that ext3 will replay 18 the journal (and thus write to the partition) even when 19 mounted "read only". Mount options "ro,noload" can be 20 used to prevent writes to the filesystem. 21 22 journal=update Update the ext3 file system's journal to the current 23 format. 24 25 journal=inum When a journal already exists, this option is ignored. 26 Otherwise, it specifies the number of the inode which 27 will represent the ext3 file system's journal file. 28 29 journal_path=path 30 journal_dev=devnum When the external journal device's major/minor numbers 31 have changed, these options allow the user to specify 32 the new journal location. The journal device is 33 identified through either its new major/minor numbers 34 encoded in devnum, or via a path to the device. 35 36 norecovery Don't load the journal on mounting. Note that this forces 37 noload mount of inconsistent filesystem, which can lead to 38 various problems. 39 40 data=journal All data are committed into the journal prior to being 41 written into the main file system. 42 43 data=ordered (*) All data are forced directly out to the main file 44 system prior to its metadata being committed to the 45 journal. 46 47 data=writeback Data ordering is not preserved, data may be written 48 into the main file system after its metadata has been 49 committed to the journal. 50 51 commit=nrsec (*) Ext3 can be told to sync all its data and metadata 52 every 'nrsec' seconds. The default value is 5 seconds. 53 This means that if you lose your power, you will lose 54 as much as the latest 5 seconds of work (your 55 filesystem will not be damaged though, thanks to the 56 journaling). This default value (or any low value) 57 will hurt performance, but it's good for data-safety. 58 Setting it to 0 will have the same effect as leaving 59 it at the default (5 seconds). 60 Setting it to very large values will improve 61 performance. 62 63 barrier=<0|1(*)> This enables/disables the use of write barriers in 64 barrier (*) the jbd code. barrier=0 disables, barrier=1 enables. 65 nobarrier This also requires an IO stack which can support 66 barriers, and if jbd gets an error on a barrier 67 write, it will disable again with a warning. 68 Write barriers enforce proper on-disk ordering 69 of journal commits, making volatile disk write caches 70 safe to use, at some performance penalty. If 71 your disks are battery-backed in one way or another, 72 disabling barriers may safely improve performance. 73 The mount options "barrier" and "nobarrier" can 74 also be used to enable or disable barriers, for 75 consistency with other ext3 mount options. 76 77 user_xattr Enables Extended User Attributes. Additionally, you 78 need to have extended attribute support enabled in the 79 kernel configuration (CONFIG_EXT3_FS_XATTR). See the 80 attr(5) manual page and http://acl.bestbits.at/ to 81 learn more about extended attributes. 82 83 nouser_xattr Disables Extended User Attributes. 84 85 acl Enables POSIX Access Control Lists support. 86 Additionally, you need to have ACL support enabled in 87 the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL). 88 See the acl(5) manual page and http://acl.bestbits.at/ 89 for more information. 90 91 noacl This option disables POSIX Access Control List 92 support. 93 94 reservation 95 96 noreservation 97 98 bsddf (*) Make 'df' act like BSD. 99 minixdf Make 'df' act like Minix. 100 101 check=none Don't do extra checking of bitmaps on mount. 102 nocheck 103 104 debug Extra debugging information is sent to syslog. 105 106 errors=remount-ro Remount the filesystem read-only on an error. 107 errors=continue Keep going on a filesystem error. 108 errors=panic Panic and halt the machine if an error occurs. 109 (These mount options override the errors behavior 110 specified in the superblock, which can be 111 configured using tune2fs.) 112 113 data_err=ignore(*) Just print an error message if an error occurs 114 in a file data buffer in ordered mode. 115 data_err=abort Abort the journal if an error occurs in a file 116 data buffer in ordered mode. 117 118 grpid Give objects the same group ID as their creator. 119 bsdgroups 120 121 nogrpid (*) New objects have the group ID of their creator. 122 sysvgroups 123 124 resgid=n The group ID which may use the reserved blocks. 125 126 resuid=n The user ID which may use the reserved blocks. 127 128 sb=n Use alternate superblock at this location. 129 130 quota These options are ignored by the filesystem. They 131 noquota are used only by quota tools to recognize volumes 132 grpquota where quota should be turned on. See documentation 133 usrquota in the quota-tools package for more details 134 (http://sourceforge.net/projects/linuxquota). 135 136 jqfmt=<quota type> These options tell filesystem details about quota 137 usrjquota=<file> so that quota information can be properly updated 138 grpjquota=<file> during journal replay. They replace the above 139 quota options. See documentation in the quota-tools 140 package for more details 141 (http://sourceforge.net/projects/linuxquota). 142 143 Specification 144 ============= 145 Ext3 shares all disk implementation with the ext2 filesystem, and adds 146 transactions capabilities to ext2. Journaling is done by the Journaling Block 147 Device layer. 148 149 Journaling Block Device layer 150 ----------------------------- 151 The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed 152 to add journaling capabilities to a block device. The ext3 filesystem code 153 will inform the JBD of modifications it is performing (called a transaction). 154 The journal supports the transactions start and stop, and in case of a crash, 155 the journal can replay the transactions to quickly put the partition back into 156 a consistent state. 157 158 Handles represent a single atomic update to a filesystem. JBD can handle an 159 external journal on a block device. 160 161 Data Mode 162 --------- 163 There are 3 different data modes: 164 165 * writeback mode 166 In data=writeback mode, ext3 does not journal data at all. This mode provides 167 a similar level of journaling as that of XFS, JFS, and ReiserFS in its default 168 mode - metadata journaling. A crash+recovery can cause incorrect data to 169 appear in files which were written shortly before the crash. This mode will 170 typically provide the best ext3 performance. 171 172 * ordered mode 173 In data=ordered mode, ext3 only officially journals metadata, but it logically 174 groups metadata and data blocks into a single unit called a transaction. When 175 it's time to write the new metadata out to disk, the associated data blocks 176 are written first. In general, this mode performs slightly slower than 177 writeback but significantly faster than journal mode. 178 179 * journal mode 180 data=journal mode provides full data and metadata journaling. All new data is 181 written to the journal first, and then to its final location. 182 In the event of a crash, the journal can be replayed, bringing both data and 183 metadata into a consistent state. This mode is the slowest except when data 184 needs to be read from and written to disk at the same time where it 185 outperforms all other modes. 186 187 Compatibility 188 ------------- 189 190 Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. 191 Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as 192 Ext2. 193 194 195 External Tools 196 ============== 197 See manual pages to learn more. 198 199 tune2fs: create a ext3 journal on a ext2 partition with the -j flag. 200 mke2fs: create a ext3 partition with the -j flag. 201 debugfs: ext2 and ext3 file system debugger. 202 ext2online: online (mounted) ext2 and ext3 filesystem resizer 203 204 205 References 206 ========== 207 208 kernel source: <file:fs/ext3/> 209 <file:fs/jbd/> 210 211 programs: http://e2fsprogs.sourceforge.net/ 212 http://ext2resize.sourceforge.net 213 214 useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html 215 http://www.ibm.com/developerworks/library/l-fs8/index.html