[ Saturday, 31 May 2008, optimizationkit ]
Lately I have described ok_defrag — a simple tool for defragmenting Linux file systems. Today, I want to describe a specialized program designed to defrag the new Ext4 file system.
(For all who would like to say that Linux file systems don’t require defragmenting: Please redirect your great ideas to the Ext4 developers. They are the authors of this program — I do not have anything in common with it. As it will turn out, Ext4 is indeed quite different than other Linux file systems. Thanks in advance for your understanding )
To begin playing with e4defrag we must start compile of new kernel with patches needed to carry out the defragmentation. Below you will find a short description of that process, and if you would not like to use all those experimental patches for Ext4, then you should be interested in these seven only:
ext4-online-defrag-exchange-blocks-between-two-inodes.patch ext4-online-defrag-relocate-file-data.patch ext4-online-defrag-alloc-contiguous-blks.patch ext4-online-defrag-ext4-defrag.patch ext4-online-defrag-for-relevant-files.patch ext4-online-defrag-check-for-freespace-fragmentation.patch ext4-online-defrag-move-victim-files.patch
In first step we start from creation of directory, grabbing the kernel source, and downloading and unpacking needed patches.
mkdir linux-2.6-ext4 cd linux-2.6-ext4/ ketchup -G 2.6-git wget http://www.kernel.org/pub/linux/kernel/people/tytso/\\ ext4-patches/2.6.26-rc2-git5-ext4-1/broken-out.tar.bz2 tar xjvf broken-out.tar.bz2 mv broken-out patches
Then we apply the patches on the sources.
quilt push -a
Then we start a process of configuring/building our new system kernel.
cp /our/beloved/.config . cp /our/beloved/script/for/building/system/kernel/build.sh .
(on my PC it look like this:)
#!/bin/sh VER=`ketchup -m` make sudo make modules_install sudo cp arch/x86/boot/bzImage /boot/vmlinuz-$VER sudo cp System.map /boot/System.map-$VER sudo /sbin/new-kernel-pkg --mkinitrd --depmod --install $VER ) make oldconfig ./build.sh
Meanwhile, when our new kernel compiles, we may open file: linux-2.6-ext4/patches/ext4-online-defrag-command.patch in our text editor of choice and we delete all lines from 1 to 18, and then from 1932 to 1935. Then, we copy our source code to other location.
cp linux-2.6-ext4/patches/ext4-online-defrag-command.patch e4defrag.c
gcc -Wall e4defrag.c -o e4defrag
It is worth to grab some tools to handle the Ext4 file systems (the very latest version from the code repository).
git-clone git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git cd e2fsprogs ./configure make make install
After running our system with brand new kernel for the first time, we can finally start to test e4defrag. First we create and mount a test file system.
dd if=/dev/zero of=fs.img bs=256M count=1 /sbin/mkfs.ext3 fs.img
Now we must allow the use of experimental code on that partition.
/sbin/debugfs -w fs.img debugfs 1.41-WIP (27-Apr-2008) debugfs: set_super_value s_flags 4 debugfs: quit
Now our new file system is ready to be mounted
mount -t ext4dev -o loop,extents fs.img /mnt/loop0/
How to cause fragmentation at Ext4? – I have not yet tested any good way for fast fragmenting Ext4. This file system contrary to other Linux file systems is exceptionally resistant to fragmentation.
/sbin/fsck.ext3 -nfv fs.img e2fsck 1.41-WIP (27-Apr-2008) First course: checking i-nodes, blocks and sizes Second course: checking directory structure Third course: checking communications directories Fourth course: checking counters appeals Fifth course: checking the summary information about groups 368 inodes used (0.56%) 1 non-contiguous inode (0.3%) number i-nodes with blocks ind/dind/tind: 136/129/129 202885 blocks used (77.39%) 0 bad blocks 0 large files 351 regular files 8 directories 0 character device files 0 block device files 0 fifos 0 links 0 symbolic links (0 fast symbolic links) 0 sockets -------- 359 files
It seems that Ext4 is a tough row to hoe, but its developers still deliver a defragmentation tool for it. Take a peep!
With use e4defrag we can defrag single files, for example:
or all directories:
e4defrag -r /patch/to/directory/
also, there is a way to defrag a partition:
e4defrag /dev/sda1 e4defrag file_system_image.img
E4defrag contrary to other solutions – Con Kolivas defrag or ok_defrag is a true professional program designed to defrag Ext file system — it does not use a simple tricks with moving files, but it checks where on a drive the free blocks are located and then moves the data into those places.
A user, who will be capable to fragment Ext4, surely will be satisfied with the results of e4defrag. I am fully satisfied with the Ext4, for now I have no need to run e4d or even ok_defrag .
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