Ext2Fsd has limited EXT4 support and by default it will load the filesystems in read-only mode, but you can force this if you really have to write on EXT4 partitions from Windows (this is not recommended). Using it, your EXT partitions will be displayed just like native NTFS or FAT partitions, being accessible from Windows Explorer.

BTRFS support for the installer came in Ubuntu 10.10 Maverick Meerkat a few days ago so the folks @ Phoronix ran some tests comparing BTRFS and EXT4.

The results between BTRFS with the default options and EXT4 were pretty close but once the zlib compression was activated (this feature is only available for BTRFS), BTRFS was 2x faster than EXT4 in the 4GB write IOzone test and 4x faster than EXT4 for the 4GB read IOzone test.

Check out the full tests results @ Phoronix.


Update: the results for this test may be wrong. Also, it seems BTRFS has a serious bug. Read the comments below!

[image credits: Phoronix]

If you are one of those people and you don't want to miss out using the new ext4 file system, there is a way to convert your existing ext3 file system to ext4.

Please note that converting-to/using ext4 is by no means necessary, you are not missing out if you are using ext3 (hell, ext2 is still widely in use). So only do this if you like to hack and get your hands dirty.

Before starting, take a look at the known issues with ext4!

Step one:
Upgrade to Jaunty. You now have a working jaunty install running the ext3 file system.

Step two:
Make a backup of all your (important) data. You can use fwbackups or any other app.
Step three:
Boot from a (jaunty) live-cd and run the following code (in this example the partition to convert is on /dev/sda1) to convert the partition:

sudo bashtune2fs -O extents,uninit_bg,dir_index /dev/sda1e2fsck -pf /dev/sda1

Step four:
Mount the partition and change the type of the converted partition in fstab:

sudo bashmount -t ext4 /dev/sda1 /mntnano /mnt/etc/fstab

change "ext3" to "ext4" like in the example below:

# /dev/sda1UUID=XXXXXXXXXXXXXXXXXXXXXXXXXX /               ext3    relatime,errors=remount-ro 0       1

change it to:

# /dev/sda1UUID=XXXXXXXXXXXXXXXXXXXXXXXXXX /               ext4    relatime,errors=remount-ro 0       1

and save the changes.

Step five:
This step might be optional but when I upgraded from Intrepid to Jaunty the upgrade process did not install/update the new grub stage. So if you don't run either of the following code examples you might get an (fatal) error 13 when booting the machine.
Use this code to refresh grub when you do not have a separate /boot partition (in this example the root partition is sda1)

sudo bashmount /dev/sda1 /mntgrub-install /dev/sda --root-directory=/mnt --recheck

Use this code to refresh grub when you do have a separate /boot partition (in this example the /boot partition is sda1)

sudo bashmkdir /mnt/bootmount /dev/sda1 /mnt/bootgrub-install /dev/sda --root-directory=/mnt --recheck

That's it, after you reboot you you will be running from an ext4 file system.
As a side note, all the files that where present before the conversion will not benefit from the conversion as they were written to disk using ext3 technology. Only newly created or overwritten files will be using the true ext4 technology (so now, using update-manager will be extra beneficial). As ext3 and ext4 are compatible with each other having files written to disk in ext3 mode on your ext4 file system do not impose any risks (and most if not all ext3 sectors could eventually disappear even without defragging).

There is currently a online-defragging tool in development (e4defrag) which should be available with the next kernel release.

Credits: whoop user @ ubuntuforums.org