Re: 2.5 Gbps PCIe card

In some ways, I kinda despise the 802.3bz specification for 2.5 and 5 Gbps on twisted pair. It came into existence after 10 Gbps twisted-pair was standardized, and IMO exists only as a reaction to the stubbornly high price of 10 Gbps ports and the lack of adoption -- 1000 Mbps has been a mainstay and is often more than sufficient.

802.3bz is only defined for twisted pair and not fibre. So there aren't too many xcvrs that support it, and even fewer SFP+ ports will accept such xcvrs. As a result, the cheap route of buying an SFP+ card and a compatible xcvr is essentially off-the-table.

The only 802.3bz compatible PCIe card I've ever personally used is an Aquantia AQN-107 that I bought on sale in 2017. It has excellent support in Linux, and did do 10 Gbps line rate by my testing.

That said, I can't imagine that cards that do only 2.5 Gbps would somehow be less performant. 2.5 Gbps hardware is finding its way into gaming motherboards, so I would think the chips are mature enough that you can just buy any NIC and expect it to work, just like buying a 1000 Mbps NIC.

BTW, some of these 802.3bz NICs will eschew 10/100 Mbps support, because of the complexity of retaining that backwards compatibility. This is almost inconsequential in 2024, but I thought I'd mention it.