Holy shit i think you and the above comment, along with this thread, may have finally given me the answer to one of the few problems i was never able to solve.

About 4-5 years ago, i was working on a project, and part of that was copying big amounts of data to a system via nfs. At 30 minutes exactly, nfs would croak, transfer fails.

I think this buffer fill and empty flow was fucking killing it. Its a shame i dont work there anymore, id definitely wanna try tweaking these settings and see if i could solve it