[lordlimecat]

Sfp isn't copper vs fiber. It's just the standard for a modular plug on network hardware.

They have 25gbe twinax SFP28s that, as far as I'm aware, have essentially identical performance specs to using optical SFP28s with fiber. The fiber is thinner and can go further, but it also is more fragile and limited on bends. Latency is almost entirely driven by the switch and the NIC.

Photons in fiber do not move meaningfully faster than signals in copper, and speed of light in short datacenters runs is not the limiting factor In latency. Any meaningful processing will happen in electronics and converting from copper to fiber introduces more latency.

There's a good paper on it here: https://www.commscope.com/globalassets/digizuite/2799-latenc...

Tldr coax actually is faster (0.77c) than optical fiber (0.67c).

[nwiswell]

> Photons in fiber do not move meaningfully faster than signals in copper, and speed of light in short datacenters runs is not the limiting factor In latency. Any meaningful processing will happen in electronics and converting from copper to fiber introduces more latency.

My understanding is that it has nothing to do with the speed of light for short-run cables. 10GBase-T uses block encoding that adds a couple microseconds of latency (which dwarfs the impact of the speed of light at short distances) and fiber (including SFP+) doesn't need to.

Coax/twinax may not need the encoding schemes that twisted pair does, I'm not sure.