Supercomputers - Does the Cabling Matter?

papaia asks: "Having watched, for a while, the development in the area of high-density server hardware solutions (i.e. blade servers), like IBM's 'top gun', and their increased presence in Data Centers, I have been wondering if anybody has had any experience (thus comments) in regards to how important - in such highly priced solutions - is (or could be) the [always neglected] cabling, connecting the servers. One such comment caught my attention, in this regard. Slashdot, how important is the server cabling infrastructure in your Data Centers, and how do you resolve the cable management aspect of it?"

Comments

Reliability

[Leroy_Brown242]

I think that it'd be fairly important. Even if only for reliability. Because speed and reliability are equally important.

literally speaking, no

[St. Arbirix]

Literally speaking the cabling won't matter at all. Whether the resistance of your wires is high or low the electrons are going to travel through it at the same rate. What may be a worry is freak occurances of inductance between wires which could possibly mess with your data, but I'm not sure how common that is. The signal is digital so it's going to be either a 1 or a 0 depending on the voltage of the line, and it's usually difficult to make the voltage do something as drastic as go from +5 to 0 or +5 to -5.

I always have to laugh anytime I go to the store and look at the number of things that say digital nowadays. Wal-Mart sells digital telephone cable for your computer to connect to the wall as if 5 feet of high quality cabling with gold plated tips is going to make a difference in the 30-odd mile trip to your ISP. A friend of mine boasted his "digital" headphones to me once and I had to beat him down to the opinion that "there must be something better about them, so I'm happy" (this sort of pacifist optimism is the bane of IT in general).

Best Buy sells Monster digital audio cables at something like $20 for a 5-ft cable. I had to argue with my father trying to convince him that the cheap RCA cables we already had back at home would be perfectly capable of communicated a digital signal the 5 inches between the DVD player and the receiver. I could have ripped two wires from a speaker cable to connect the two devices and would have gotten just as good sound.

People don't seem to want to realize that digital implies lossless or error-corrected. They don't understand that the "premium quality sound" transmitted between devices can be done using the cheapest electronics equipment available.

I'd save a fortune on car stereo...

Re:literally speaking, no

[alienw]

Well, actually, SPDIF requires 6MHz bandwidth. As far as the 75 ohm impedance: I didn't pull it out of my ass, it's specified by the relevant standard (IEC958), and it's not some kind of audiophile debate. Basically, it's the impedance of standard TV coax. Pick up any book about radio and read about impedances. Here's a link to a short description of SPDIF, in case you are curious: here.

As for your link: don't believe everything you read. The Audioholics article shows many gross misunderstandings. For instance, the reason direction is marked on some high-end cables is for optimal grounding, not because cable manufacturers don't know audio is AC. Also, they seem to have failed physics when they claim that a battery cannot do anything if the circuit is not complete. Ever hear of FETs?

Cable quality certainly makes a difference for just about any application, including audio. Even a "digital" protocol like USB imposes a number of requirements on the cable quality. Cable quality for sensitive analog signals is even more critical. If you have a few hundred thousand dollars' worth of test equipment, you can probably quantify the differences, calculate bit error rates, and so on. It's easier to just listen, though.

Yes, and documentation

[rueger]

In any setting the quality of cabling does matter. Or, more specifically, the quality of the connectors on the cable, and the quality of their installation.

Anyone who argues otherwise should recall that the first step in troubleshooting is almost invariably to check the cables.

While I am happy to use zip cord to wire my stereo speakers, I wouldn't trust dollar store cables for anything mission critical.

More important though is to document your cable runs, or even better tag each cable so that you have some idea where it begins and ends. You may know what goes into and out of that big ball of CAT-5 on the floor, but the guy who follows you will have no idea.