Since the Ubuntu Lucid upgrade, suspend/resume is not working any more on my desktop, which means I must powercycle every day. This leads to a higher fsck rate on my mounted filesystems, and as those are increasing in size over time, this takes a long time to boot. This is why I decided to migrate everything to ext4, thereby offering me faster fsck times, and an overall better performance.
The procedure to migrate ext3 volumes to ext4 is quite straightforward :
For non-root filesystems :
First, unmount the partition.
umount /dev/sda5
Next, run a filesystem check on it to make sure it is in sane condition. We are still on ext3.
fsck.ext3 -pf /dev/sda5
Enable new features of ext4 on the filesystem.
tune2fs -O extents,uninit_bg,dir_index /dev/sda5
Option "extents" enables the filesystem to use extents instead of bitmap mapping for files, "uninit_bg" reduces file system check times by only checking used portions of the disk, and "dir_index" allows storing the contents of large directories in a htree for faster access. Option "dir_index" is also supported by ext3, so you may already be using it, but it makes no harm to specify it here.
Run a filesystem check. It will find errors. It is normal. Let it fix them.
fsck.ext4 -yfD /dev/sda5
The "-D" parameter will actually enable the "dir_index" option by rebuilding directory index. It can be rebuilt (optimized) at any later time by running the check with the parameter.
Now edit your /etc/fstab file to say "ext4" instead of "ext3" for /home. Other options may differ for your system.
/dev/sda5 /home ext4 defaults 0 2
Try to mount your new ext4 filesystem.
mount /home
If it succeeds, congratulations.
It may seem that the migration from ext3 to ext4 is now complete, and it is almost true. Except that any old files created before the conversion will continue using the bitmap mapping of ext3 instead of extents of ext4. Files will eventually migrate to the new format as they are updated during normal system operation, because on next write they will be saved using extents. Unfortunately many frequently used files (like application binaries) are often read and rarely written to. The outcome is that the files will remain using the old format for a long time, and you will not be able to experience full potential of ext4. Modifying attributes with chattr can be done on multiple files. Although digging trough the entire directory system is not really feasible, so you can use some of the shell magic to accomplish the task.
find /home -xdev -type f -print0 | xargs -0 chattr +e
For root filesystems :
You will need to use a Linux liveCD, or the installation CD that came with your distribution. You might want to check if the kernel on that installation medium has ext4 capabilities. Simply follow the above procedure, but don't forget to change /etc/fstab first, so your root partition is marked as ext4.
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