I couldn't really find data on my external HDD WD32001032-001
but somehow think it is USB 2.0 and even 7200 rpm. The PC network card is 100 Mbit, or even 1000 Mbit. the router is 100 Mbit. So having something with 12 Mbit (USB 1.1. speed) might explain it.
the router seems to have USB 2.0
Is there a way to test a HDD what USB it has? the WD website didn't give any information. but the slowest i saw there in the legacy section is USB 2.0