So I connected an external drive to the T3200M router and used it as a network drive by following this instruction (link)
For some reason, the router wipes the external drive and all data on it is gone if I disconnect and reconnect the external drive.
It also happened sometimes if I reboot the router or reset the router to default setting.
Is there any ways to prevent this happening?
You would be better to set it up as a sharable drive on one of the always-on computers on your network. Few have had success using the USB port on the T3200M for a network drive.