I am trying to test the maximum throughput of my network adapters and switches, I have two 10Gb 570SFP+ Adapters in one server, and two of the same adapters in the other server. I have tried using the tool NTttcp using these commands
ntttcp.exe -s -m 8,*,10.10.1.2 -l 2M -a 2 -t 30
ntttcp.exe -s -m 8,*,10.10.5.2 -l 2M -a 2 -t 30
and for the receiver
ntttcp.exe -r -m 8,*,10.10.1.2 -rb 2M -a 16 -t 30
ntttcp.exe -r -m 8,*,10.10.5.2 -rb 2M -a 16 -t 30
I have a stacked HP 2920 switches (2 in a stack one side, and 2 in another stack the other), the switches are linked together via two fibre optics. I have already tested all adapters on an individual basis and I can get 10Gbps from one side to the other. However the switches are configured in such a way which are supposed to allow me to combine those two 10Gbps fibres and get me 20Gbps, however when I run the NTttcp tool for both adapters at the same time, i only get a maximum throughput of 10Gbps between the two adapters, not 10Gbps on each adapter. HP seem to think it's because the sending server can not send more than 10Gbps of data, however if i ran each of those commands at the same time in their own separate command window, i thought each command would max out each adapter. HP are asking if there is any way to increase the server's maximum sending throughput, i have already ran those commands with 2M, 20M and 50M but it doesn't make any difference.
The image attached shows how the switches and network are connected. the thin red lines are the 10Gbps adapters to the servers, the thick red lines are the fibre optics which link the two buildings (these are OM4 cables, which provide 10Gbps each)