This is not possible - you must unmount to change the
data journalling mode.
> >From alan post...
> 
> Don't refuse unneccessarily on remount with     (Petr
> Vandrovec)
>                               data= option with ext3
> 
> it means that I can do a remount an already mounted
> ext3 FS and change the data mode?
No, this refers to a problem where
	mount foo -o data=journal
would succeed, but then
	mount foo -o remount,data=journal
would fail.  We now allow remount to specify the journalling
mode, but it must be the same as the current mode - this change
is just to allow us to work more nicely with the mount tools.
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