So I am playing around with my Raspberry Pi and Pi Noir camera. One of the limitations of the Pi (if you even want to consider it a "limitation") is the fact that it runs off an SD Card. While not a problem in and of itself, it means that I only a limited amount of storage space on the Pi. My solution to this was to simply throw in a 16GB USB stick.
It took a bit of experimenting to find the right way to do this... There were a variety of mount commands I tried using, and while they technically got the USB mounted, the motion daemon had all kinds of issues writing to the USB stick. Finally I got the right mount command to work, and motion was able to write to the USB stick! I turned it off, placed the setup elsewhere to capture some images, and when it booted back up, the mount point was gone... I had completely forgotten that anything mounted with the mount command after boot, will not be there on reboot.
I was going to lose it... I had literally wasted that whole time. And to top it off, I did NOT make note of the good mount command, so could not reproduce it. So as frustrating as it was, it was a bit of a good thing as it forced me to find another solution.
Enter the fstab file. Again, it took a number of tries to find the right combination of settings to make the USB stick writeable by the motion daemon. Here is the final entry that I am using, which seems to be working just fine.
/dev/sda1 /mnt/usb vfat user,umask=0000 0 0