I have two DELL PCs each installed Intel X520-DA1 with SFP+ (FTLX1471D3BCV-IT) and using single mode fiber to connect two PCs directly, on Windows 7 ultimate 64bit the adapter linked as 10Gbps, but when I using iperf to test the transmission speed, it only ran about 2.5Gbps, I change two adapters to X520-LR1 and still the same?!
No matter what I change (configurations, SFP+), the speed still extremely slow,I wonder what could be wrong?!