10GbE connection problem, speeds limited in one direction
10GbE connection problem, speeds limited in one direction
Hello everyone, I'm facing a problem with my 10Gb Ethernet configuration. I have two PCs—my main machine and an Unraid server—both equipped with the Asus XG-C100C 10G card. The speed is only reaching full capacity in one direction. When I run iperf and set my PC as the server, I see speeds around 10G. But when I switch roles and make the Unraid box the server, the connection drops significantly. Testing file transfers confirms this: moving data to/from an NVMe drive is fast, but pulling from the cache back to the PC is slow. I'm getting 700MB to 900MB per second in each direction, which is much lower than expected. I've tried adjusting the TCP window size in iperf and it helps a bit, but I'm still not seeing consistent full speeds both ways. Could there be a specific setting on either system that affects this behavior?
I've been checking this setup with my TrueNAS Scale and Windows 11 desktop. Results fluctuate a lot—ranging from 6 to 9 Gbps depending on timing. When I run a WSL2 Ubuntu instance as the iperf client and TrueNAS as the server, I see close to 10 Gbps. However, without port forwarding, I can't verify this in WSL as the server side. I created about a 10GB file and copied it both ways; each transfer stayed above 9 Gbps. Are you seeing similar patterns where the connection doesn’t hit its full potential?
It seems you're checking for issues with the Linux kernel. Are you noticing any specific problems or bugs lately?
When moving files from Windows to Unraid, speeds range around 700MB to 900MB per second. Transferring in the opposite direction maintains a steady 1.15GB per second. Both drives support high performance, exceeding 2000MB per second for both reads and writes.
I'm wondering if there might be a caching problem on the Windows machine or some extra overhead. Are the PCIe lanes fully utilized? Could your PC have multiple devices sharing a PCIe lane, which might be causing the issue? It seems those two Ethernet cards are PCI 2, but if they're on a shared lane it could be disrupting performance. Try relocating one of the cards to another slot. It's odd you're seeing speeds above 1GB/sec but below 10GB/sec. You might want to experiment with different cables on the Windows box just for testing.