That sounds fine, but what is the actually did command you are running? A simple dd if=/dev/zero of=/dev/sdf bs=1m should be all you need. If you are using dd, run iotop or something similar in the background to see if there’s any writing actually happen.

When you say dd “stops” does it just quit? If so it might be the dock briefly disconnecting, you should be able to see this happen by watching dmesg with dmesg -w as you are running your dd command.