I've tried 2 different USB drives on my Model 3, both properly formatted for FAT32 with TeslaCam folder and nothing else. The first was not fast enough - the 3 gave me an error message saying so. However, its rated speed WAS fast enough. But no sweat - I believe the error msg my 3 gave me.
I tried a faster drive recommended on one of the Tesla user sites. Worked fine for a few days, then during a drive the dashcam icon entirely disappeared and Sentry failed to record. I checked the drive on my Win10 pc -- it had errors and needed "repair," so I let Windows do that. (Same deal as the first USB drive.) Tried it again, worked a couple of days, then same problem - no dashcam icon. But this time I got no error msg from my 3 about drive speed. Checked the drive again - it had recorded for a couple of days. The files are there. But it was corrupted again.
My 2 USB ports have only a phone cable connected to one (no splitter) and the USB in the other. I tried the USB in each of the ports.
Going to try one more time, but this is getting old! I see others have had the exact same problem. Is Tesla addressing this?