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Why do we use facilities with EPO's?
I was complaining to some of the power designers during the building of a major facility that the EPO button represented a single point of failure, and effectively made all of the redundancy built into the power system useless. After all, what's the point of having two (or more) of anything, if there's one button somewhere that turns it all off? What I found interesting is that a single EPO is not a hard and fast rule. They walked me through a twisty maze of the national electric code, the national fire code, and local regulations. Through that journey, they left me with a rather interesting tidbit. The more "urban" an area the more likely it is to have strict fire codes. Typically these codes require a single EPO for the entire structure, there's no way to compartmentalize to rooms or subsystems. However in more rural areas this is often not so, and they had in fact built data centers to code WITHOUT a single building EPO in several locations. That's to say there was no EPO, but that it may only affect a single room, or even a single device. If they can be avoided, why do we put up with them? Do we really want our colo in downtown San Francisco bad enough to take the risk of having a single point of failure? How can we, as engineers, ask questions about how many generators, how much fuel, and yet take for granted that there is one button on the wall that makes it all turn off? Is it simply that having colo in the middle of the city is so convenient that it overrides the increased cost and the reduced redundancy that are necessitated by that location? -- Leo Bicknell - bicknell@xxxxxxx - CCIE 3440 PGP keys at http://www.ufp.org/~bicknell/ Read TMBG List - tmbg-list-request@xxxxxxxx, www.tmbg.org