I've got the D750 with two 64gig SD cards in it, set in the menu options as write to card 1, backup to card 2.
Does anyone know what happens if I harvest off my images from card 1, and never touch card 2?
When card 2 fills up, does it overwrite oldest? (would seem logical to me) or stop backing up / writing to / once full?
Up to this point in my workflow, once I've grabbed the images off card 1, backed them up locally (laptop, NAS), I stick it back in the camera, format both with a two button push function and away I go.