(resolved) Owncloud data filepath

A symlink is created during the DietPi installation of Owncloud. This automatically points /var/www/owncloud/data to:
USB Drive install = /mnt/usb_1/owncloud
Non-USB drive install = /owncloud

If you run the following, you should see owncloud data files on your USB drive:

ls -lha /mnt/usb_1/owncloud