I made a copy of everything on the card, but didn't remove everything, though I was in a housekeeping mood and did dump quite a few photos. Defrag is a considerably less drastic move than the format. I'll use the camera some and see what happens. You're correct, the camera can do a format of the card. I didn't defrag through the card reader, I had the camera on the cable so it did it while the camera and the computer were connected and both turned on.