Intel XL710-QDA2 in PCIe 4.0 x2 Slot?

I want to directly connect two computers using two Intel XL710-QDA2 40Gbps PCIe 3.0 x8 cards. However, the only slot I have available on my MSI x670-P Wi-Fi motherboard is a PCIe 4.0 x 2 slot (the physical slot size is x16).

If the card I would put in the other computer is in a PCIe 3.0 x 16 slot, does this mean I will get 10 Gbps speeds (since the Intel card is x8 but would be limited to a x2 on the MSI motherboard)? Or would it not function at all, or at a different speed?

I did a similar test on these computers using Mellanox Connect-X2 10G SFP+ cards and I was getting about 500 MB/sec in the PCIe 4.0 x2 slot, which was higher than the 250 I expected given those cards are PCIe 2.0 x8 (I think).

You will have the lowest protocol that either the card or the motherboard supports with the physical amount of lanes that are present. PCIe3.0x8 card in PCIe4.0x2 slot will negotiate a PCIe3.0x2 connection. PCIe3.0x1 is 985MB/s so twice that would amount to about 16190Mbits.

This all is based on what you gave me, I want to note that I’ve never seen a PCIe x2 connection though, it’s either x1, x4, x8 or x16. But maybe in the space of professional server equipment x2 also does exist, I am not sure.

Also PCIe2.0x1 is 500 MB/s!

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