back to my orig. question: I got an answer:

I assumed that RAID is on top of the fs, but I got told that actually the fs is on top of the RAID module. Therefore there is only *one* fs "instance" involved, which either gets rolled back or not.

However, a new question arises now: If a journaling fs gives savety on power failure, but a raid software is in between, does it probably break your power off savety for the sake of HD HW failure savety?