Howto Convert Ext3 filesystem to Ext4 Filesystem without Reinstalling OS in Fedora/CentOS/Ubuntu

Things to remember

• Unmount the filesystem before convert
• Filesystem must be non-root

This way you can improve the performance, storage limits and features of your existing filesystem without reformatting and/or reinstalling your OS and softwares.
First, unmount the partition: umount /dev/sda2 (change sda2 with your Drive)
Next, run a filesystem check on it to make sure it is in sane condition.

fsck.ext3 -pf /dev/sda2

Enable new features of ext4 on the filesystem

tune2fs -O extents,uninit_bg,dir_index  /dev/sda2

Run a filesystem check. to make sure that the filesystem is now clean.

fsck -pf /dev/sda2

Now edit your /etc/fstab file and replace "ext3" with "ext4" for /dev/sda1. Other options may differ for your system.

/dev/sda2  /disk ext4 defaults 0 2

Try to mount your new ext4 filesystem: mount /disk