From: Theodore Ts'o Subject: [PATCH 32/52] ext4: Documentation updates. Date: Sat, 5 Jul 2008 13:35:58 -0400 Message-ID: <1215279378-30504-33-git-send-email-tytso@mit.edu> References: <1215279378-30504-1-git-send-email-tytso@mit.edu> <1215279378-30504-2-git-send-email-tytso@mit.edu> <1215279378-30504-3-git-send-email-tytso@mit.edu> <1215279378-30504-4-git-send-email-tytso@mit.edu> <1215279378-30504-5-git-send-email-tytso@mit.edu> <1215279378-30504-6-git-send-email-tytso@mit.edu> <1215279378-30504-7-git-send-email-tytso@mit.edu> <1215279378-30504-8-git-send-email-tytso@mit.edu> <1215279378-30504-9-git-send-email-tytso@mit.edu> <1215279378-30504-10-git-send-email-tytso@mit.edu> <1215279378-30504-11-git-send-email-tytso@mit.edu> <1215279378-30504-12-git-send-email-tytso@mit.edu> <1215279378-30504-13-git-send-email-tytso@mit.edu> <1215279378-30504-14-git-send-email-tytso@mit.edu> <1215279378-30504-15-git-send-email-tytso@mit.edu> <1215279378-30504-16-git-send-email-tytso@mit.edu> <1215279378-30504-17-git-send-email-tytso@mit.edu> <1215279378-30504-18-git-send-email-tytso@mit.edu> <1215279378-30504-19-git-send-email-tytso@mit.edu> <1215279378-30504-20-git-send-email-tytso@mit.edu> <1215279378-30504-21-git-send-email-tytso@mit.edu> <1215279378-30504-22-git-send-email-tytso@mit.edu> <1215279378-30504-23-git-send-email-tytso@mit.edu> <1215279378-30504-24-git-send-email-tytso@mit.edu> <1215279378-30504-25-git-send-email-tytso@mit.edu> <1215279378-30504-26-git-send-email-tytso@mit.edu> <1215279378-30504-27-git-send-email-tytso@mit.edu> <1215279378-30504-28-git-send-email-tytso@mit.edu> <1215279378-30504-29-git-send-email-tytso@mit.edu> <1215279378-30504-30-git-send-email-tytso@mit.edu> <1215279378-30504-31-git-send-email-tytso@mit.edu> <1215279378-30504-32-git-send-email-tytso@mit.edu> Cc: "Jose R. Santos" , "Theodore Ts'o" To: Ext4 Developers List , Linux Kernel Developers List Return-path: Received: from www.church-of-our-saviour.ORG ([69.25.196.31]:33019 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754189AbYGERg2 (ORCPT ); Sat, 5 Jul 2008 13:36:28 -0400 In-Reply-To: <1215279378-30504-32-git-send-email-tytso@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: From: Jose R. Santos Some of the information in Documentation/filesystems/ext4.txt is out of date and in need of an update.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 Signed-off-by: "Theodore Ts'o" --- 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@vger.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: 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