Hello
you can save dude data , webproxy-cache , usermanager data to usb storage.
i test RB751uHnD usb port and connect my WD 1TB hard disk and my router detect it!
but i do not format it because i need my data
for printing log i think best way is sending log to a Syslog server like kiwi or dude or solarwinds or mikrotik syslog!