1. I do have a partition with a partitions.conf with the following content :
Default=0x7fff,ipoib,mtu=5:ALL=full;
2. By specifications the HP DDR 4x IB Switch Module supports 4k MTU, but it's not really manageable, so it might be the switch's fault after all. I am waiting for a new Topspin switch, so if that is the problem it will be resolved.
3 and 4. I am going to update the drivers today, tho I can see the infiniband ports as ConnectX family adapters. So I guess the firmware and the HCA itself supports 4k. But still I will do some reserach in that direction too.
Thanks a lot. I will keep you guys updated and if anyone has any other ideas - please shoot. I really want to get this thing going so I can test the virtual storage.