Why we don't use cable management arms

October 5, 2007

One of the things I discovered when I came here was that while cable management arms came standard with many of the servers we bought, we weren't using them; in fact, when we moved servers that had them, we tended to remove them. This surprised me a bit, since they're generally a part of a well organized rack, and I recently got around to asking my co-workers about this.

It turns out that there is a simple reason: heat dissipation. Our racks are all open racks, so our servers are cooled with plain front to back airflow, and it turns out that a populated cable management arm effectively blocks this. In the days when we used them, my co-workers noticed that the rear of those servers were real hot-spots, significantly warmer than the surrounding air. However nice the organization and neatness is, we'd rather have cool servers.

(It seems that cable management arms work best in enclosed racks where you're using vertical cooling, with cold air forced in at the bottom and exhaust fans at the top to pull out the hot air.)

In general, the more I've been here the more I've come to feel that, however much I like admiring them, the conventional wisdom represented by nicely organized racks are the results of being able to plan your racks, build them mostly at one time, and not have things change all the time. This is not how things are here; even when we have a plan for a rack we usually don't get all the hardware at once, and things change all the time (sometimes rapidly). In this environment, things like those neatly and tightly tied cable bundles are a disaster waiting to happen the next time you need to change things, or at least an annoyance; they look good only so long as you don't need to touch them.

(The same thing holds true for cable labels; much like comments in computer programs, their presence may delude you into believing them.)

You can probably maintain such neatness even in an environment of uncertainty and change, but it has a definite cost in time (and thus in money), one that we cannot justify.

(Having said that, I should probably neaten up a server or two of mine, or at least figure out what the best way to run their cables is.)

Written on 05 October 2007.
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Last modified: Fri Oct 5 22:27:58 2007
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