[e12e]

While I wasn't aware you could get them that cheap, I think I'd still look into second hand infiniband for home use. Allows the use of copper for short (pc-to-pc, point-to-point) distances. While optic is absolutely cool, as far as I can tell a single 1m patch cable will cost ~80 USD -- quite a lot considering the cost of the NIC... And even in IBM's sales brochure for their optical switch, infiband comes out a little ahead:

http://www-01.ibm.com/common/ssi/cgi-bin/ssialias?infotype=S...

[wmf]

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.

[e12e]

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:

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.

[DiabloD3]

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.

[kijiki]

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.