I have added 10Gbe cards to my Windows desktop and my Unraid server and connected them directly to one another. Transferring to the server works pretty good, although I think it should be faster. It tends to stay in the 500MB/s range. That's going to a NVMe drive that supports upwards of 3200MB/s, also I have 64GB of ram and an i7, so there's no bottleneck there.  Copying from the array is very slow though. I realize that's probably hitting the drives, but I've used iperf3 and there's definitely a problem.  

[  5][TX-C]   0.00-1.00   sec  1.08 GBytes  9.30 Gbits/sec    0   3.97 MBytes

[  7][RX-C]   0.00-1.00   sec  19.8 KBytes   162 Kbits/sec
[  5][TX-C]   1.00-2.00   sec  1.08 GBytes  9.31 Gbits/sec    0   3.97 MBytes

[  7][RX-C]   1.00-2.00   sec  11.3 KBytes  92.7 Kbits/sec
[  5][TX-C]   2.00-3.00   sec  1.09 GBytes  9.34 Gbits/sec    0   3.97 MBytes

[  7][RX-C]   2.00-3.00   sec  21.2 KBytes   174 Kbits/sec
[  5][TX-C]   3.00-4.00   sec  1.05 GBytes  9.05 Gbits/sec    0   3.97 MBytes

 

At times I can't even get the bidirectional test to run, and I've had issues connecting them. For a while I couldn't even get a traceroute to run from the server to the desktop, although the desktop works fine. Now the traceroute is showing the single hop and it's 0.2ms. Disabling the firewall on the windows box has seemed to help that. 

 

Both computers have 2.5gbps cards also that are on the main network, and they are on different subnets (192.168.0 for the 2.5, 10.0.0 for the 10Gbe). 

iperf results point to a LAN problem, could be NICs, cables, transceiver, etc.