[Richard Rodriguez]"Question: can a 16 or 8 gig cards be formatted while rolling on the other card? "
Yes you can. I just tried it to make sure. I was recording on the SxS Pro card in slot 1 and successfully formatted the card in slot 2. Knowing this you could probably use the "delete all clips" function on the other card as an alternative to the formatting command.
Formating can be done but be aware of the risk. If one card is recording, formating the other cards is pretty easy. If you're not recording you may very well make the mistake of formating the wrong card.
My preferred workflow is to Delete All Clips in the ClipBrowser after offloading the clips. This way the camera gets a clean card which can be helpful if you're cutting it close to the "rollover" point.
For me, formating the cards (or deleting clips in camera) happens before the shoot. Once in shoot mode I don't want to tax my brain by making sure the camera is pointing at the right card fore a format or a delete.
Or risk knocking or otherwise jostling the camera while it's recording. Any noise from touching the camera will also be transmitted directly into the on camera mic (if active) and recorded. All in all, it's just not advisable to do anything that would compromise the recording quality. It's difficult enough trying to swap cards during a long shoot without adding to your stress levels by trying to format cards too.