40GbE uses approximately the same copper cables as Infiniband. There's probably more used IB equipment floating around than used 40GbE, but otherwise I'd go with Ethernet.
Ah, of course. I was misled by wikipedia[1], but it should've been obvious that the same connection could be used for both inifinband and ethernet. So, indeed, there are copper interconnects:
Actually seems the price is finally coming down a bit (compared to what I remember these used to cost, years ago -- but maybe I've just upped my budget ;-).
"The Quad Small Form-factor Pluggable (QSFP) is a compact, hot-pluggable transceiver used for data communications applications. It interfaces networking hardware to a fiber optic cable."
But it also interfaces hardware to copper cables, as I gather.
The cable you're looking for is called a direct connect cable. "Fake" optical modules on both sides, plugs it together with a permanently wired copper cable.
DAC is a common term for this. Direct Attached Copper.
It is a SFP+ plug on each end (but without all the optical magic), connected with twin-ax cable, which is like coax but with 2 signal paths, one for each direction.
http://www.amazon.co.uk/Mellanox-3-3ft-QSFP-QSFP-Passive-Cop...
Actually seems the price is finally coming down a bit (compared to what I remember these used to cost, years ago -- but maybe I've just upped my budget ;-).
[1] http://en.wikipedia.org/wiki/QSFP
"The Quad Small Form-factor Pluggable (QSFP) is a compact, hot-pluggable transceiver used for data communications applications. It interfaces networking hardware to a fiber optic cable."
But it also interfaces hardware to copper cables, as I gather.