From Eeebuntuwiki

Turn your EXT3 partition into a EXT4 partition

So. You just installed eeebuntu 3.0 and have the benefits of EXT4 on your root partition but not your home? Didn't want to format the home drive as you wanted to save your data? DONT FEAR!

EXT3 can be mounted as EXT4 using afew tweak to the OS in the LIVECD enviroment.

You wont see the benefits of ext right away as anything which was on the drive will still be written with ext4. Its when you start putting new data on you'll see the difference!

Upgrading to Ext4

So we need to boot into our liveCD via the USB and go to System->Partition Editor.

This will show all the partition in your hard disk. Record down the filesystem ID of the partition that you want to convert to ext4.

Close the Partition Editor. Open a terminal, type the following:

sudo tune2fs -O extents,uninit_bg,dir_index /dev/XXXX

Replace XXXX by the filesystem ID that you have recorded just now.

Once that is done, type the following to fixed your partition:

sudo fsck -pf /dev/XXXX

Don’t forget to replace XXXX with your filesystem ID.

Mount your filesystem

sudo mount -t ext4 /dev/XXXX /mnt

Open the fstab file

gksu gedit /mnt/etc/fstab

and change the ext3 entry to ext4. Save and exit.

Edit fstab

Back to the terminal, we need to reinstall the grub bootloader.

sudo grub-install /dev/XXX

This time, replace the XXX by the filesystem without the number. For example, sudo grub-install /dev/sda

Close the terminal and restart the computer. Reboot into Eeebuntu.

In the terminal, type

df -T

You should now see your filesystem mounted as EXT4!

Enjoy your faster write speeds :)