A homelab user found that 10GbE file transfers were crawling at 100-200 Mbps. After ruling out the NAS, RAID, and SMB, they tested directly between two PCs with iperf3 and still saw poor speeds. The culprit was the Intel E610-XT2 NIC's receive buffers set to the default 512.
Increasing them to 4096 boosted receive throughput from 1.33 Gbit/s to 5.15 Gbit/s. Transmit was still slow until they disabled Large Send Offload (LSO) V2 for IPv4, which jumped transmit from 313 Mbit/s to 7.03 Gbit/s. The lesson: when network speed is unexpectedly low, check NIC driver settings like receive buffers and LSO before blaming other components.
The fix is simple and can be done via PowerShell or the adapter properties.
Source: Hacker News · Summarized by HeadlinesBriefing