Some people already found out the hard way that simply changing the /etc/fstab to make the root filesystem use the journal writeback modus will break the system.
The trick to enable this feature is relative simple and involves 1 aditional step to editing the /etc/fstab
Lets use the below /etc/fstab snippet to illustrate the steps involved
/dev/sda5 / defaults 0 0
We change this /etc/fstab snippet to:
/dev/sda5 / data=writeback 0 0
And we execute the following command:
tune2fs -O journal_data_writeback /dev/sda5