this has been, to me, one of the most fascinating nanog threads in years. at the moment my own datacenter problem is filtration. isc lives in a place where outside air is quite cool enough for server inlet seven or more months out of the year. we've also got quite high ceilings. a 2HP roof fan will move 10000 cubic feet per minute. we've got enough make-up air for that. but, the filters on the make-up air have to be cleaned several times a week, and at the moment that's a manual operation. mechanical systems, by comparison, only push 20% make-up air, and the filters seem to last a month or more between maintainance events. i'm stuck with the same question that vexes the U S Army when they send the M1A1 into sandstorms, or that caused a lot of shutdowns in NYC in the days after 9/11: what kind of automation can i deploy that will precipitate the particulates so that air can move (for cooling) and so that air won't bring grit (which is conductive)? -- Paul Vixie