Is my math correct about PCIe bandwidht and 10Gbps NICs ?

[mcury]

Math for slot PCIe 3.0 x4 |10 Gbps NIC PCI 3.0 x4

Network card:
10 (Gbps) = 1.25 GB/s per second in half-duplex or 2.5GB/s full-duplex.

10Gbps NIC full duplex = 2.5GB/s
SLOT PCIe 3.0 x4 = 8GB/s

Conclusion: If I get a 10 Gbps NIC PCIe 3.0 x4, it will use 2.5GB/s full duplex which won't be throttled by the PCIe slot. I could even get a two slot card because it would use 5GB/s maximum of the 8GB/s of the slot.

Math for slot PCIe 3.0 x4 | 10 Gbps NIC PCI 2.0 x8 (it will run in PCIe 2.0 x4).

Network card:
10 (Gbps) = 1.25 GB/s per second in half-duplex or 2.5GB/s full-duplex.

10Gbps NIC full duplex = 2.5GB/s
SLOT PCIe 2.0 x4 = 4GB/s

Conclusion: If I get a 10Gbps NIC PCIe 2.0 x8 and run it on PCI 2.0 x4, it will use 2.5GB/s full duplex, which won't be throttled by the PCIe slot.
I could get a dual port 10Gbps NIC but it would be throttled by the slot in about 1GB/s.

[stephenw10]

@mcury said in Is my math correct about PCIe bandwidht and 10Gbps NICs ?:

I could get a dual port 10Gbps NIC but it would be throttled by the slot in about 1GB/s.

Only if you are trying to use both ports at full duplex. Which very rarely happens IMO.

[mcury]

@stephenw10 said in Is my math correct about PCIe bandwidht and 10Gbps NICs ?:

Only if you are trying to use both ports at full duplex. Which very rarely happens IMO.

Thanks Stephen, I will get one of those..

I have an AMD B550 chipset, which the DMI connection (from chipset to CPU), is PCI 3.0 x4.
I have doing some math with that also, and even using a NVME PCI 3.0 and a few SATA drives, won't saturate that link with this NIC (single port).
I have also a NVME PCIe 4.0, but that is directly connected to the CPU, so no chipset lanes used here.

I will use it in my server, connect it directly to a USW-Enterprise-PoE-8 switch through a DAC cable since local users will be connecting to it using 2.5Gbps ports, and also some connections from the Internet.