1 2Ext3 Filesystem 3=============== 4 5Ext3 was originally released in September 1999. Written by Stephen Tweedie 6for the 2.2 branch, and ported to 2.4 kernels by Peter Braam, Andreas Dilger, 7Andrew Morton, Alexander Viro, Ted Ts'o and Stephen Tweedie. 8 9Ext3 is the ext2 filesystem enhanced with journalling capabilities. 10 11Options 12======= 13 14When mounting an ext3 filesystem, the following option are accepted: 15(*) == default 16 17ro 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 22journal=update Update the ext3 file system's journal to the current 23 format. 24 25journal=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 29journal_path=path 30journal_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 36norecovery Don't load the journal on mounting. Note that this forces 37noload mount of inconsistent filesystem, which can lead to 38 various problems. 39 40data=journal All data are committed into the journal prior to being 41 written into the main file system. 42 43data=ordered (*) All data are forced directly out to the main file 44 system prior to its metadata being committed to the 45 journal. 46 47data=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 51commit=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 63barrier=<0|1(*)> This enables/disables the use of write barriers in 64barrier (*) the jbd code. barrier=0 disables, barrier=1 enables. 65nobarrier 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 77user_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 83nouser_xattr Disables Extended User Attributes. 84 85acl 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 91noacl This option disables POSIX Access Control List 92 support. 93 94reservation 95 96noreservation 97 98bsddf (*) Make 'df' act like BSD. 99minixdf Make 'df' act like Minix. 100 101check=none Don't do extra checking of bitmaps on mount. 102nocheck 103 104debug Extra debugging information is sent to syslog. 105 106errors=remount-ro Remount the filesystem read-only on an error. 107errors=continue Keep going on a filesystem error. 108errors=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 113data_err=ignore(*) Just print an error message if an error occurs 114 in a file data buffer in ordered mode. 115data_err=abort Abort the journal if an error occurs in a file 116 data buffer in ordered mode. 117 118grpid Give objects the same group ID as their creator. 119bsdgroups 120 121nogrpid (*) New objects have the group ID of their creator. 122sysvgroups 123 124resgid=n The group ID which may use the reserved blocks. 125 126resuid=n The user ID which may use the reserved blocks. 127 128sb=n Use alternate superblock at this location. 129 130quota These options are ignored by the filesystem. They 131noquota are used only by quota tools to recognize volumes 132grpquota where quota should be turned on. See documentation 133usrquota in the quota-tools package for more details 134 (http://sourceforge.net/projects/linuxquota). 135 136jqfmt=<quota type> These options tell filesystem details about quota 137usrjquota=<file> so that quota information can be properly updated 138grpjquota=<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 143Specification 144============= 145Ext3 shares all disk implementation with the ext2 filesystem, and adds 146transactions capabilities to ext2. Journaling is done by the Journaling Block 147Device layer. 148 149Journaling Block Device layer 150----------------------------- 151The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed 152to add journaling capabilities to a block device. The ext3 filesystem code 153will inform the JBD of modifications it is performing (called a transaction). 154The journal supports the transactions start and stop, and in case of a crash, 155the journal can replay the transactions to quickly put the partition back into 156a consistent state. 157 158Handles represent a single atomic update to a filesystem. JBD can handle an 159external journal on a block device. 160 161Data Mode 162--------- 163There are 3 different data modes: 164 165* writeback mode 166In data=writeback mode, ext3 does not journal data at all. This mode provides 167a similar level of journaling as that of XFS, JFS, and ReiserFS in its default 168mode - metadata journaling. A crash+recovery can cause incorrect data to 169appear in files which were written shortly before the crash. This mode will 170typically provide the best ext3 performance. 171 172* ordered mode 173In data=ordered mode, ext3 only officially journals metadata, but it logically 174groups metadata and data blocks into a single unit called a transaction. When 175it's time to write the new metadata out to disk, the associated data blocks 176are written first. In general, this mode performs slightly slower than 177writeback but significantly faster than journal mode. 178 179* journal mode 180data=journal mode provides full data and metadata journaling. All new data is 181written to the journal first, and then to its final location. 182In the event of a crash, the journal can be replayed, bringing both data and 183metadata into a consistent state. This mode is the slowest except when data 184needs to be read from and written to disk at the same time where it 185outperforms all other modes. 186 187Compatibility 188------------- 189 190Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. 191Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as 192Ext2. 193 194 195External Tools 196============== 197See manual pages to learn more. 198 199tune2fs: create a ext3 journal on a ext2 partition with the -j flag. 200mke2fs: create a ext3 partition with the -j flag. 201debugfs: ext2 and ext3 file system debugger. 202ext2online: online (mounted) ext2 and ext3 filesystem resizer 203 204 205References 206========== 207 208kernel source: <file:fs/ext3/> 209 <file:fs/jbd/> 210 211programs: http://e2fsprogs.sourceforge.net/ 212 http://ext2resize.sourceforge.net 213 214useful links: http://www.ibm.com/developerworks/library/l-fs7/index.html 215 http://www.ibm.com/developerworks/library/l-fs8/index.html 216