@louis2 These are the only 2 machines talking to each other at the same time? Then it isn't a problem, your acks are going to go on the same wire as well now.. So you would never be able to see full throughput. be it that small.
Your talking about a optimization of jumbo, but then are not caring about your overall bandwidth being reduced.
What if you have machines C and D talking to each other on a completely different vlans - but they share the same wire now. Or could be.
If your happy with your setup.. Have at it.
All of that aside - you still haven't shown that your disks can read/write at the extra throughput jumbo could bring.. If the disks can not write/read even bandwidth X (standard 1500).. Does it make any sense to complex up the network with jumbo to gain that extra speed jumbo could provide?
There is no freaking way jumbo gives you this sort of boost
speed.jpg
You have something else going on there.. If you are only seeing 3.2 on 1500, and 9.4 on jumbo.