Documentation / filesystems / ext3.txt
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Based on kernel version 2.6.33. Page generated on 2010-02-24 15:36 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_dev=devnum When the external journal device's major/minor numbers 30 have changed, this option allows the user to specify 31 the new journal location. The journal device is 32 identified through its new major/minor numbers encoded 33 in devnum. 34 35 norecovery Don't load the journal on mounting. Note that this forces 36 noload mount of inconsistent filesystem, which can lead to 37 various problems. 38 39 data=journal All data are committed into the journal prior to being 40 written into the main file system. 41 42 data=ordered (*) All data are forced directly out to the main file 43 system prior to its metadata being committed to the 44 journal. 45 46 data=writeback Data ordering is not preserved, data may be written 47 into the main file system after its metadata has been 48 committed to the journal. 49 50 commit=nrsec (*) Ext3 can be told to sync all its data and metadata 51 every 'nrsec' seconds. The default value is 5 seconds. 52 This means that if you lose your power, you will lose 53 as much as the latest 5 seconds of work (your 54 filesystem will not be damaged though, thanks to the 55 journaling). This default value (or any low value) 56 will hurt performance, but it's good for data-safety. 57 Setting it to 0 will have the same effect as leaving 58 it at the default (5 seconds). 59 Setting it to very large values will improve 60 performance. 61 62 barrier=1 This enables/disables barriers. barrier=0 disables 63 it, barrier=1 enables it. 64 65 orlov (*) This enables the new Orlov block allocator. It is 66 enabled by default. 67 68 oldalloc This disables the Orlov block allocator and enables 69 the old block allocator. Orlov should have better 70 performance - we'd like to get some feedback if it's 71 the contrary for you. 72 73 user_xattr Enables Extended User Attributes. Additionally, you 74 need to have extended attribute support enabled in the 75 kernel configuration (CONFIG_EXT3_FS_XATTR). See the 76 attr(5) manual page and http://acl.bestbits.at/ to 77 learn more about extended attributes. 78 79 nouser_xattr Disables Extended User Attributes. 80 81 acl Enables POSIX Access Control Lists support. 82 Additionally, you need to have ACL support enabled in 83 the kernel configuration (CONFIG_EXT3_FS_POSIX_ACL). 84 See the acl(5) manual page and http://acl.bestbits.at/ 85 for more information. 86 87 noacl This option disables POSIX Access Control List 88 support. 89 90 reservation 91 92 noreservation 93 94 bsddf (*) Make 'df' act like BSD. 95 minixdf Make 'df' act like Minix. 96 97 check=none Don't do extra checking of bitmaps on mount. 98 nocheck 99 100 debug Extra debugging information is sent to syslog. 101 102 errors=remount-ro Remount the filesystem read-only on an error. 103 errors=continue Keep going on a filesystem error. 104 errors=panic Panic and halt the machine if an error occurs. 105 (These mount options override the errors behavior 106 specified in the superblock, which can be 107 configured using tune2fs.) 108 109 data_err=ignore(*) Just print an error message if an error occurs 110 in a file data buffer in ordered mode. 111 data_err=abort Abort the journal if an error occurs in a file 112 data buffer in ordered mode. 113 114 grpid Give objects the same group ID as their creator. 115 bsdgroups 116 117 nogrpid (*) New objects have the group ID of their creator. 118 sysvgroups 119 120 resgid=n The group ID which may use the reserved blocks. 121 122 resuid=n The user ID which may use the reserved blocks. 123 124 sb=n Use alternate superblock at this location. 125 126 quota These options are ignored by the filesystem. They 127 noquota are used only by quota tools to recognize volumes 128 grpquota where quota should be turned on. See documentation 129 usrquota in the quota-tools package for more details 130 (http://sourceforge.net/projects/linuxquota). 131 132 jqfmt=<quota type> These options tell filesystem details about quota 133 usrjquota=<file> so that quota information can be properly updated 134 grpjquota=<file> during journal replay. They replace the above 135 quota options. See documentation in the quota-tools 136 package for more details 137 (http://sourceforge.net/projects/linuxquota). 138 139 bh (*) ext3 associates buffer heads to data pages to 140 nobh (a) cache disk block mapping information 141 (b) link pages into transaction to provide 142 ordering guarantees. 143 "bh" option forces use of buffer heads. 144 "nobh" option tries to avoid associating buffer 145 heads (supported only for "writeback" mode). 146 147 148 Specification 149 ============= 150 Ext3 shares all disk implementation with the ext2 filesystem, and adds 151 transactions capabilities to ext2. Journaling is done by the Journaling Block 152 Device layer. 153 154 Journaling Block Device layer 155 ----------------------------- 156 The Journaling Block Device layer (JBD) isn't ext3 specific. It was designed 157 to add journaling capabilities to a block device. The ext3 filesystem code 158 will inform the JBD of modifications it is performing (called a transaction). 159 The journal supports the transactions start and stop, and in case of a crash, 160 the journal can replay the transactions to quickly put the partition back into 161 a consistent state. 162 163 Handles represent a single atomic update to a filesystem. JBD can handle an 164 external journal on a block device. 165 166 Data Mode 167 --------- 168 There are 3 different data modes: 169 170 * writeback mode 171 In data=writeback mode, ext3 does not journal data at all. This mode provides 172 a similar level of journaling as that of XFS, JFS, and ReiserFS in its default 173 mode - metadata journaling. A crash+recovery can cause incorrect data to 174 appear in files which were written shortly before the crash. This mode will 175 typically provide the best ext3 performance. 176 177 * ordered mode 178 In data=ordered mode, ext3 only officially journals metadata, but it logically 179 groups metadata and data blocks into a single unit called a transaction. When 180 it's time to write the new metadata out to disk, the associated data blocks 181 are written first. In general, this mode performs slightly slower than 182 writeback but significantly faster than journal mode. 183 184 * journal mode 185 data=journal mode provides full data and metadata journaling. All new data is 186 written to the journal first, and then to its final location. 187 In the event of a crash, the journal can be replayed, bringing both data and 188 metadata into a consistent state. This mode is the slowest except when data 189 needs to be read from and written to disk at the same time where it 190 outperforms all other modes. 191 192 Compatibility 193 ------------- 194 195 Ext2 partitions can be easily convert to ext3, with `tune2fs -j <dev>`. 196 Ext3 is fully compatible with Ext2. Ext3 partitions can easily be mounted as 197 Ext2. 198 199 200 External Tools 201 ============== 202 See manual pages to learn more. 203 204 tune2fs: create a ext3 journal on a ext2 partition with the -j flag. 205 mke2fs: create a ext3 partition with the -j flag. 206 debugfs: ext2 and ext3 file system debugger. 207 ext2online: online (mounted) ext2 and ext3 filesystem resizer 208 209 210 References 211 ========== 212 213 kernel source: <file:fs/ext3/> 214 <file:fs/jbd/> 215 216 programs: http://e2fsprogs.sourceforge.net/ 217 http://ext2resize.sourceforge.net 218 219 useful links: http://www.ibm.com/developerworks/library/l-fs7.html 220 http://www.ibm.com/developerworks/library/l-fs8.html
- [ filesystems ]
- 00-INDEX
- 9p.txt
- adfs.txt
- affs.txt
- afs.txt
- autofs4-mount-control.txt
- automount-support.txt
- befs.txt
- bfs.txt
- btrfs.txt
- [ caching ]
- cifs.txt
- coda.txt
- [ configfs ]
- cramfs.txt
- debugfs.txt
- dentry-locking.txt
- devpts.txt
- directory-locking
- dlmfs.txt
- dnotify.txt
- ecryptfs.txt
- exofs.txt
- ext2.txt
- ext3.txt
- ext4.txt
- fiemap.txt
- files.txt
- fuse.txt
- gfs2-glocks.txt
- gfs2-uevents.txt
- gfs2.txt
- hfs.txt
- hfsplus.txt
- hpfs.txt
- inotify.txt
- isofs.txt
- jfs.txt
- Locking
- locks.txt
- mandatory-locking.txt
- ncpfs.txt
- [ nfs ]
- nilfs2.txt
- ntfs.txt
- ocfs2.txt
- omfs.txt
- [ pohmelfs ]
- porting
- proc.txt
- quota.txt
- ramfs-rootfs-initramfs.txt
- relay.txt
- romfs.txt
- seq_file.txt
- sharedsubtree.txt
- smbfs.txt
- spufs.txt
- squashfs.txt
- sysfs-pci.txt
- sysfs.txt
- sysv-fs.txt
- tmpfs.txt
- ubifs.txt
- udf.txt
- ufs.txt
- vfat.txt
- vfs.txt
- xfs.txt
- xip.txt
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