I bought a pair of 3TB MyBook Live NAS drives and plugged them into a GigaBit switch in my Mac environment.
I upgraded the firmware, changed the IP to static and then waited. And waited. And waited.
Everything ground to a crawl and one drive wouldn’t stop spinning (even two days later).
The issue, if you’ve got this problem, was the Twonky app in the Settings/Media tab (enabled by default).
I turned it off and everything’s back to normal. Mind you I had to uplug one drive while I changed the setting on the second.
So it would appear two Twonky’s on the same network is a recipe for disaster.
Hope this helps.