I'm running a Mellanox MCX311A-XCAT CX311A card in a PCI-E 2.0x1 slot right now on AMD's X470 platform. I'm able to get just over 3Gb/sec on an iperf run.
I've only been running it for a few weeks on windows but the hardware seems happy running in this fashion. You'd have to determine though if a ConnectX-3 card will work well with TrueNAS/BSD. This particular hardware does work in the slot config you are asking about at least.
Thank for your reply, firworks. The speed is enough in my case.
My network are using Mellanox ConnectX-2 (PCIe 2.0 x8), one in my PC (AMD B450 Platform, Chipset PCIe 2.0 x4) and another in my pfSense router (Intel H67 Platform, CPU PCIe 3.0 x16). MTU is 9000 in pfSense and 9014 in PC (Windows 10). I can get around 7 Gbit/s in short period and 6 Gbit/s in long period.
Code:
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 850 MBytes 7.13 Gbits/sec
[ 4] 1.00-2.00 sec 934 MBytes 7.83 Gbits/sec
[ 4] 2.00-3.00 sec 916 MBytes 7.68 Gbits/sec
[ 4] 3.00-4.00 sec 925 MBytes 7.76 Gbits/sec
[ 4] 4.00-5.00 sec 917 MBytes 7.69 Gbits/sec
[ 4] 5.00-6.00 sec 910 MBytes 7.63 Gbits/sec
[ 4] 6.00-7.00 sec 914 MBytes 7.66 Gbits/sec
[ 4] 7.00-8.00 sec 952 MBytes 7.98 Gbits/sec
[ 4] 8.00-9.00 sec 928 MBytes 7.78 Gbits/sec
[ 4] 9.00-10.00 sec 925 MBytes 7.76 Gbits/sec
[ 4] 10.00-11.00 sec 936 MBytes 7.85 Gbits/sec
[ 4] 11.00-12.00 sec 926 MBytes 7.77 Gbits/sec
[ 4] 12.00-13.00 sec 905 MBytes 7.59 Gbits/sec
[ 4] 13.00-14.00 sec 937 MBytes 7.86 Gbits/sec
[ 4] 14.00-15.00 sec 895 MBytes 7.51 Gbits/sec
[ 4] 15.00-16.00 sec 936 MBytes 7.85 Gbits/sec
[ 4] 16.00-17.00 sec 926 MBytes 7.77 Gbits/sec
[ 4] 17.00-18.00 sec 910 MBytes 7.63 Gbits/sec
[ 4] 18.00-19.00 sec 942 MBytes 7.90 Gbits/sec
[ 4] 19.00-20.00 sec 911 MBytes 7.64 Gbits/sec
[ 4] 20.00-21.00 sec 934 MBytes 7.83 Gbits/sec
[ 4] 21.00-22.00 sec 929 MBytes 7.79 Gbits/sec
[ 4] 22.00-23.00 sec 922 MBytes 7.73 Gbits/sec
[ 4] 23.00-24.00 sec 923 MBytes 7.74 Gbits/sec
[ 4] 24.00-25.00 sec 948 MBytes 7.96 Gbits/sec
[ 4] 25.00-26.00 sec 927 MBytes 7.77 Gbits/sec
[ 4] 26.00-27.00 sec 946 MBytes 7.94 Gbits/sec
[ 4] 27.00-28.00 sec 934 MBytes 7.83 Gbits/sec
[ 4] 28.00-29.00 sec 956 MBytes 8.02 Gbits/sec
[ 4] 29.00-30.00 sec 969 MBytes 8.13 Gbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-30.00 sec 27.1 GBytes 7.77 Gbits/sec sender
[ 4] 0.00-30.00 sec 27.1 GBytes 7.77 Gbits/sec receiver
Code:
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-521.02 sec 388 GBytes 6.39 Gbits/sec sender
[ 4] 0.00-521.02 sec 0.00 Bytes 0.00 bits/sec receiver