Both the XF100 and XF300 can record to both cards in parallel (effectively turning them into a mirrored RAID), but do we know precisely what happens if one card fails during recording? Does the camera continue? Is there an error? Has anybody experienced this yet?

The manual says: "If a CF card becomes full during double slot recording, recording on both cards will stop. On the other hand, if an error occurs with one of the cards, recording will continue on the other card."

Interesting.

I guess that you could test this by opening the little door & popping out one of the cards while recording.

With an XF105, I tried dual recording such that one card ran out of space. The other card continued recording.