On Wed, Jul 02, 2008 at 12:22:00PM -0500, Jose R. Santos wrote:
> 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>
Here are some changes I have added to further update/correct/clarify
the ext4.txt file:
- Ted
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 4424266..574c96a 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -13,40 +13,45 @@ Mailing list: linux-ext4@xxxxxxxxxxxxxxx
1. Quick usage instructions:
===========================
- - Grab updated e2fsprogs from
+ - Compile and install the latest version of e2fsprogs (at least
+ 1.41-WIP-0617) from:
+
ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs-interim/
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:
+ - Create a new filesystem using the ext4dev filesystem type:
- # mke2fs -j -E test_fs /dev/hda1
+ # mke2fs -t ext4dev /dev/hda1
- Or set the test_fs flag on an existing ext3 filesystem:
+ 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:
- # debugfs -w /dev/sda5
- debugfs 1.41-WIP (17-Jun-2008)
- debugfs: set_super_value s_flags 4
- debugfs: quit
+ # tune2fs -O extents -E test_fs /dev/hda1
- - Mounting:
+ If the filesystem was created with 128 byte inodes, it can be
+ converted to use 256 byte for greater efficiency via:
- # mount /dev/hda1 /wherever -t ext4dev
+ # tune2fs -I 256 /dev/hda1
- - To disable extents:
+ (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.)
- # mount /dev/hda1 /wherever -t ext4dev -o noextents
+ - Mounting:
- - The filesystem is compatible with the ext3 driver until you add a file
- which has extents (ie: `mount -o extents', then create a file).
+ # 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
===========
@@ -67,17 +72,13 @@ Mailing list: linux-ext4@xxxxxxxxxxxxxxx
* ability to pack bitmaps and inode tables into larger virtual groups via the
flex_bg feature
* large file support
-
-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
+* Inode allocation using large virtual block groups via flex_bg
-2.3 Candidate features for future inclusion
+2.2 Candidate features for future inclusion
* 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
--
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