Big discrepancy between `du` and `df` used space on USB drive

[Adam Funk]

Hi,

I'm trying to figure out why the card on a bike camera is fuller than
the files on it. Can anyone explain this?

/media/adam$ df -h HANDLEBAR/
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        29G   12G   18G  39% /media/adam/HANDLEBAR

/media/adam$ du -sh HANDLEBAR/
3.3G	HANDLEBAR/

The second one matches the result of adding up the files and `du`s of
subdirectories in that directory (including one hidden file of
117K). The camera has a micro SD card with a vfat filesystem.

Thanks
Adam