From: Jose R. Santos <jrs@xxxxxxxxxx>
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Some of the information in Documentation/filesystems/ext4.txt is out
of date and in need of an update.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@xxxxxxxxxx>
--
Documentation/filesystems/ext4.txt | 83 +++++++++++++++++++++---------------
1 files changed, 49 insertions(+), 34 deletions(-)
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 0c5086d..b0c3bb2 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -15,23 +15,32 @@ Mailing list: linux-ext4@xxxxxxxxxxxxxxx
- 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
- ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/
- - It's still mke2fs -j /dev/hda1
+ or grab the latest git repository from:
+ git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git
+
+ - Create a new filesystem and set the "test_fs" extended option:
- - mount /dev/hda1 /wherever -t ext4dev
+ # mke2fs -j -E test_fs /dev/hda1
- - To enable extents,
+ Or set the test_fs flag on an existing ext3 filesystem:
- mount /dev/hda1 /wherever -t ext4dev -o extents
+ # debugfs -w /dev/sda5
+ debugfs 1.41-WIP (17-Jun-2008)
+ debugfs: set_super_value s_flags 4
+ debugfs: quit
+
+ - Mounting:
+
+ # mount /dev/hda1 /wherever -t ext4dev
+
+ - To disable extents:
+
+ # mount /dev/hda1 /wherever -t ext4dev -o noextents
- The filesystem is compatible with the ext3 driver until you add a file
which has extents (ie: `mount -o extents', then create a file).
- 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
-
- 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
@@ -44,41 +53,46 @@ Mailing list: linux-ext4@xxxxxxxxxxxxxxx
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
+* 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
-2.1 Previously available, soon to be enabled by default by "mkefs.ext4":
+2.2 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
-2.2 Candidate features for future inclusion
+2.3 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)
+* Inode allocation using large virtual block groups via flex_bg (patch
+ available; fragmentation issues due to prolong fs use still unknown)
+* reduced mke2fs time via 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 +238,7 @@ 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 +270,8 @@ 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
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