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| -rw-r--r-- | Documentation/filesystems/ext4/ext4.rst (renamed from Documentation/filesystems/ext4.txt) | 142 |
1 files changed, 64 insertions, 78 deletions
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4/ext4.rst index 7f628b9f7c4b..9d4368d591fa 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4/ext4.rst @@ -1,6 +1,8 @@ +.. SPDX-License-Identifier: GPL-2.0 -Ext4 Filesystem -=============== +======================== +General Information +======================== Ext4 is an advanced level of the ext3 filesystem which incorporates scalability and reliability enhancements for supporting large filesystems @@ -11,37 +13,30 @@ Mailing list: linux-ext4@vger.kernel.org Web site: http://ext4.wiki.kernel.org -1. Quick usage instructions: -=========================== +Quick usage instructions +======================== Note: More extensive information for getting started with ext4 can be - found at the ext4 wiki site at the URL: - http://ext4.wiki.kernel.org/index.php/Ext4_Howto +found at the ext4 wiki site at the URL: +http://ext4.wiki.kernel.org/index.php/Ext4_Howto - - Compile and install the latest version of e2fsprogs (as of this - writing version 1.41.3) from: + - The latest version of e2fsprogs can be found at: + + https://www.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/ - http://sourceforge.net/project/showfiles.php?group_id=2406 - or - https://www.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/ + http://sourceforge.net/project/showfiles.php?group_id=2406 or grab the latest git repository from: - git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git - - - Note that it is highly important to install the mke2fs.conf file - that comes with the e2fsprogs 1.41.x sources in /etc/mke2fs.conf. If - you have edited the /etc/mke2fs.conf file installed on your system, - you will need to merge your changes with the version from e2fsprogs - 1.41.x. + https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git - Create a new filesystem using the ext4 filesystem type: - # mke2fs -t ext4 /dev/hda1 + # mke2fs -t ext4 /dev/hda1 - Or to configure an existing ext3 filesystem to support extents: + Or to configure an existing ext3 filesystem to support extents: # tune2fs -O extents /dev/hda1 @@ -50,10 +45,6 @@ Note: More extensive information for getting started with ext4 can be # tune2fs -I 256 /dev/hda1 - (Note: we currently do not have tools to convert an ext4 - filesystem back to ext3; so please do not do try this on production - filesystems.) - - Mounting: # mount -t ext4 /dev/hda1 /wherever @@ -75,10 +66,11 @@ Note: More extensive information for getting started with ext4 can be the filesystem with a large journal can also be helpful for metadata-intensive workloads. -2. Features -=========== +Features +======== -2.1 Currently available +Currently Available +------------------- * ability to use filesystems > 16TB (e2fsprogs support not available yet) * extent format reduces metadata overhead (RAM, IO for access, transactions) @@ -103,31 +95,15 @@ Note: More extensive information for getting started with ext4 can be [1] Filesystems with a block size of 1k may see a limit imposed by the directory hash tree having a maximum depth of two. -2.2 Candidate features for future inclusion - -* online defrag (patches available but not well tested) -* reduced mke2fs time via lazy itable initialization in conjunction with - the uninit_bg feature (capability to do this is available in e2fsprogs - but a kernel thread to do lazy zeroing of unused inode table blocks - after filesystem is first mounted is required for safety) - -There are several others under discussion, whether they all make it in is -partly a function of how much time everyone has to work on them. Features like -metadata checksumming have been discussed and planned for a bit but no patches -exist yet so I'm not sure they're in the near-term roadmap. - -The big performance win will come with mballoc, delalloc and flex_bg -grouping of bitmaps and inode tables. Some test results available here: - - - http://www.bullopensource.org/ext4/20080818-ffsb/ffsb-write-2.6.27-rc1.html - - http://www.bullopensource.org/ext4/20080818-ffsb/ffsb-readwrite-2.6.27-rc1.html - -3. Options -========== +Options +======= When mounting an ext4 filesystem, the following option are accepted: (*) == default +======================= ======================================================= +Mount Option Description +======================= ======================================================= ro Mount filesystem read only. Note that ext4 will replay the journal (and thus write to the partition) even when mounted "read only". The @@ -387,33 +363,38 @@ i_version Enable 64-bit inode version support. This option is dax Use direct access (no page cache). See Documentation/filesystems/dax.txt. Note that this option is incompatible with data=journal. +======================= ======================================================= Data Mode ========= There are 3 different data modes: * writeback mode -In data=writeback mode, ext4 does not journal data at all. This mode provides -a similar level of journaling as that of XFS, JFS, and ReiserFS in its default -mode - metadata journaling. A crash+recovery can cause incorrect data to -appear in files which were written shortly before the crash. This mode will -typically provide the best ext4 performance. + + In data=writeback mode, ext4 does not journal data at all. This mode provides + a similar level of journaling as that of XFS, JFS, and ReiserFS in its default + mode - metadata journaling. A crash+recovery can cause incorrect data to + appear in files which were written shortly before the crash. This mode will + typically provide the best ext4 performance. * ordered mode -In data=ordered mode, ext4 only officially journals metadata, but it logically -groups metadata information related to data changes with the data blocks into a -single unit called a transaction. When it's time to write the new metadata -out to disk, the associated data blocks are written first. In general, -this mode performs slightly slower than writeback but significantly faster than journal mode. + + In data=ordered mode, ext4 only officially journals metadata, but it logically + groups metadata information related to data changes with the data blocks into + a single unit called a transaction. When it's time to write the new metadata + out to disk, the associated data blocks are written first. In general, this + mode performs slightly slower than writeback but significantly faster than + journal mode. * journal mode -data=journal mode provides full data and metadata journaling. All new data is -written to the journal first, and then to its final location. -In the event of a crash, the journal can be replayed, bringing both data and -metadata into a consistent state. This mode is the slowest except when data -needs to be read from and written to disk at the same time where it -outperforms all others modes. Enabling this mode will disable delayed -allocation and O_DIRECT support. + + data=journal mode provides full data and metadata journaling. All new data is + written to the journal first, and then to its final location. In the event of + a crash, the journal can be replayed, bringing both data and metadata into a + consistent state. This mode is the slowest except when data needs to be read + from and written to disk at the same time where it outperforms all others + modes. Enabling this mode will disable delayed allocation and O_DIRECT + support. /proc entries ============= @@ -425,10 +406,12 @@ Information about mounted ext4 file systems can be found in in table below. Files in /proc/fs/ext4/<devname> -.............................................................................. + +================ ======= File Content +================ ======= mb_groups details of multiblock allocator buddy cache of free blocks -.............................................................................. +================ ======= /sys entries ============ @@ -439,28 +422,30 @@ Information about mounted ext4 file systems can be found in /sys/fs/ext4/dm-0). The files in each per-device directory are shown in table below. -Files in /sys/fs/ext4/<devname> +Files in /sys/fs/ext4/<devname>: + (see also Documentation/ABI/testing/sysfs-fs-ext4) -.............................................................................. - File Content +============================= ================================================= +File Content +============================= ================================================= delayed_allocation_blocks This file is read-only and shows the number of blocks that are dirty in the page cache, but which do not have their location in the filesystem allocated yet. - inode_goal Tuning parameter which (if non-zero) controls +inode_goal Tuning parameter which (if non-zero) controls the goal inode used by the inode allocator in preference to all other allocation heuristics. This is intended for debugging use only, and should be 0 on production systems. - inode_readahead_blks Tuning parameter which controls the maximum +inode_readahead_blks Tuning parameter which controls the maximum number of inode table blocks that ext4's inode table readahead algorithm will pre-read into the buffer cache - lifetime_write_kbytes This file is read-only and shows the number of +lifetime_write_kbytes This file is read-only and shows the number of kilobytes of data that have been written to this filesystem since it was created. @@ -508,7 +493,7 @@ Files in /sys/fs/ext4/<devname> in the file system. If there is not enough space for the reserved space when mounting the file mount will _not_ fail. -.............................................................................. +============================= ================================================= Ioctls ====== @@ -518,8 +503,10 @@ through the system call interfaces. The list of all Ext4 specific ioctls are shown in the table below. Table of Ext4 specific ioctls -.............................................................................. - Ioctl Description + +============================= ================================================= +Ioctl Description +============================= ================================================= EXT4_IOC_GETFLAGS Get additional attributes associated with inode. The ioctl argument is an integer bitfield, with bit values described in ext4.h. This ioctl is an @@ -610,8 +597,7 @@ Table of Ext4 specific ioctls normal user by accident. The data blocks of the previous boot loader will be associated with the given inode. - -.............................................................................. +============================= ================================================= References ========== |