mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 19:00:25 +00:00
ext4: Documentation updates.
Some of the information in Documentation/filesystems/ext4.txt is out of date and in need of an update. Signed-off-by: Jose R. Santos <jrs@us.ibm.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
parent
5f21b0e642
commit
93e3270c87
1 changed files with 62 additions and 44 deletions
|
@ -13,72 +13,89 @@ Mailing list: linux-ext4@vger.kernel.org
|
|||
1. Quick usage instructions:
|
||||
===========================
|
||||
|
||||
- Grab updated e2fsprogs from
|
||||
ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs-interim/
|
||||
This is a patchset on top of e2fsprogs-1.39, which can be found at
|
||||
- Compile and install the latest version of e2fsprogs (as of this
|
||||
writing version 1.41) from:
|
||||
|
||||
http://sourceforge.net/project/showfiles.php?group_id=2406
|
||||
|
||||
or
|
||||
|
||||
ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/
|
||||
|
||||
- It's still mke2fs -j /dev/hda1
|
||||
or grab the latest git repository from:
|
||||
|
||||
- mount /dev/hda1 /wherever -t ext4dev
|
||||
git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git
|
||||
|
||||
- To enable extents,
|
||||
- Create a new filesystem using the ext4dev filesystem type:
|
||||
|
||||
mount /dev/hda1 /wherever -t ext4dev -o extents
|
||||
# mke2fs -t ext4dev /dev/hda1
|
||||
|
||||
- The filesystem is compatible with the ext3 driver until you add a file
|
||||
which has extents (ie: `mount -o extents', then create a file).
|
||||
Or configure an existing ext3 filesystem to support extents and set
|
||||
the test_fs flag to indicate that it's ok for an in-development
|
||||
filesystem to touch this filesystem:
|
||||
|
||||
NOTE: The "extents" mount flag is temporary. It will soon go away and
|
||||
extents will be enabled by the "-o extents" flag to mke2fs or tune2fs
|
||||
# tune2fs -O extents -E test_fs /dev/hda1
|
||||
|
||||
If the filesystem was created with 128 byte inodes, it can be
|
||||
converted to use 256 byte for greater efficiency via:
|
||||
|
||||
# tune2fs -I 256 /dev/hda1
|
||||
|
||||
(Note: we currently do not have tools to convert an ext4dev
|
||||
filesystem back to ext3; so please do not do try this on production
|
||||
filesystems.)
|
||||
|
||||
- Mounting:
|
||||
|
||||
# mount -t ext4dev /dev/hda1 /wherever
|
||||
|
||||
- When comparing performance with other filesystems, remember that
|
||||
ext3/4 by default offers higher data integrity guarantees than most. So
|
||||
when comparing with a metadata-only journalling filesystem, use `mount -o
|
||||
data=writeback'. And you might as well use `mount -o nobh' too along
|
||||
with it. Making the journal larger than the mke2fs default often helps
|
||||
performance with metadata-intensive workloads.
|
||||
ext3/4 by default offers higher data integrity guarantees than most.
|
||||
So when comparing with a metadata-only journalling filesystem, such
|
||||
as ext3, use `mount -o data=writeback'. And you might as well use
|
||||
`mount -o nobh' too along with it. Making the journal larger than
|
||||
the mke2fs default often helps performance with metadata-intensive
|
||||
workloads.
|
||||
|
||||
2. Features
|
||||
===========
|
||||
|
||||
2.1 Currently available
|
||||
|
||||
* ability to use filesystems > 16TB
|
||||
* ability to use filesystems > 16TB (e2fsprogs support not available yet)
|
||||
* extent format reduces metadata overhead (RAM, IO for access, transactions)
|
||||
* extent format more robust in face of on-disk corruption due to magics,
|
||||
* internal redunancy in tree
|
||||
|
||||
2.1 Previously available, soon to be enabled by default by "mkefs.ext4":
|
||||
|
||||
* dir_index and resize inode will be on by default
|
||||
* large inodes will be used by default for fast EAs, nsec timestamps, etc
|
||||
* improved file allocation (multi-block alloc, delayed alloc)
|
||||
* fix 32000 subdirectory limit
|
||||
* nsec timestamps for mtime, atime, ctime, create time
|
||||
* inode version field on disk (NFSv4, Lustre)
|
||||
* reduced e2fsck time via uninit_bg feature
|
||||
* journal checksumming for robustness, performance
|
||||
* persistent file preallocation (e.g for streaming media, databases)
|
||||
* ability to pack bitmaps and inode tables into larger virtual groups via the
|
||||
flex_bg feature
|
||||
* large file support
|
||||
* Inode allocation using large virtual block groups via flex_bg
|
||||
|
||||
2.2 Candidate features for future inclusion
|
||||
|
||||
There are several under discussion, whether they all make it in is
|
||||
partly a function of how much time everyone has to work on them:
|
||||
* Online defrag (patches available but not well tested)
|
||||
* reduced mke2fs time via lazy itable initialization in conjuction 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)
|
||||
|
||||
* improved file allocation (multi-block alloc, delayed alloc; basically done)
|
||||
* fix 32000 subdirectory limit (patch exists, needs some e2fsck work)
|
||||
* nsec timestamps for mtime, atime, ctime, create time (patch exists,
|
||||
needs some e2fsck work)
|
||||
* inode version field on disk (NFSv4, Lustre; prototype exists)
|
||||
* reduced mke2fs/e2fsck time via uninitialized groups (prototype exists)
|
||||
* journal checksumming for robustness, performance (prototype exists)
|
||||
* persistent file preallocation (e.g for streaming media, databases)
|
||||
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.
|
||||
|
||||
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:
|
||||
|
||||
The big performance win will come with mballoc and delalloc. CFS has
|
||||
been using mballoc for a few years already with Lustre, and IBM + Bull
|
||||
did a lot of benchmarking on it. The reason it isn't in the first set of
|
||||
patches is partly a manageability issue, and partly because it doesn't
|
||||
directly affect the on-disk format (outside of much better allocation)
|
||||
so it isn't critical to get into the first round of changes. I believe
|
||||
Alex is working on a new set of patches right now.
|
||||
- http://www.bullopensource.org/ext4/20080530/ffsb-write-2.6.26-rc2.html
|
||||
- http://www.bullopensource.org/ext4/20080530/ffsb-readwrite-2.6.26-rc2.html
|
||||
|
||||
3. Options
|
||||
==========
|
||||
|
@ -224,7 +241,7 @@ stripe=n Number of filesystem blocks that mballoc will try
|
|||
disks * RAID chunk size in file system blocks.
|
||||
|
||||
Data Mode
|
||||
---------
|
||||
=========
|
||||
There are 3 different data modes:
|
||||
|
||||
* writeback mode
|
||||
|
@ -256,7 +273,8 @@ kernel source: <file:fs/ext4/>
|
|||
<file:fs/jbd2/>
|
||||
|
||||
programs: http://e2fsprogs.sourceforge.net/
|
||||
http://ext2resize.sourceforge.net
|
||||
|
||||
useful links: http://fedoraproject.org/wiki/ext3-devel
|
||||
http://www.bullopensource.org/ext4/
|
||||
http://ext4.wiki.kernel.org/index.php/Main_Page
|
||||
http://fedoraproject.org/wiki/Features/Ext4
|
||||
|
|
Loading…
Reference in a new issue