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Message-Id: <1215279378-30504-33-git-send-email-tytso@mit.edu>
Date: Sat, 5 Jul 2008 13:35:58 -0400
From: Theodore Ts'o <tytso@....edu>
To: Ext4 Developers List <linux-ext4@...r.kernel.org>,
Linux Kernel Developers List <linux-kernel@...r.kernel.org>
Cc: "Jose R. Santos" <jrs@...ibm.com>, "Theodore Ts'o" <tytso@....edu>
Subject: [PATCH 32/52] ext4: Documentation updates.
From: Jose R. Santos <jrs@...ibm.com>
Some of the information in Documentation/filesystems/ext4.txt is out
of date and in need of an update.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@...ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
Documentation/filesystems/ext4.txt | 102 ++++++++++++++++++++---------------
1 files changed, 58 insertions(+), 44 deletions(-)
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 0c5086d..77ed8fe 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -13,72 +13,85 @@ Mailing list: linux-ext4@...r.kernel.org
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/
- 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 using the ext4dev filesystem type:
+
+ # mke2fs -t ext4dev /dev/hda1
+
+ 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:
- - mount /dev/hda1 /wherever -t ext4dev
+ # tune2fs -O extents -E test_fs /dev/hda1
- - To enable extents,
+ 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 -o extents
+ # tune2fs -I 256 /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).
+ (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.)
- 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
+ - 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 +237,7 @@ 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 +269,8 @@ 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
--
1.5.6.rc3.1.g36b7.dirty
--
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