On Tue, Jun 30, 2009 at 1:36 PM, Erik Trimble<erik.trim...@sun.com> wrote: > Bob Friesenhahn wrote: >> >> On Tue, 30 Jun 2009, Neal Pollack wrote: >> >>> Actually, they do quite a bit more than that. They create jobs, generate >>> revenue for battery manufacturers, and tech's that change batteries and do >>> PM maintenance on the large units. Let's not >> >> It sounds like this is a responsibility which should be moved to the US >> federal goverment since UPSs create jobs. >> > Actually, I think UPS already employs some 410,000+ people, making it the > 3rd largest private employer in the USA. (5th overall, if you include the > Federal Gov't and the US Postal Service). > > <wink> > > >>> In the last 28 years of doing this stuff, I've found a few times that the >>> UPS has actually worked and lasted as long as the outage. >> >> I have seen UPSs help quite a lot for short glitches lasting seconds, or a >> minute. Otherwise the outage is usually longer than the UPSs can stay up >> since the problem required human attention. >> >> A standby generator is needed for any long outages. >> >> Bob >> -- >> Bob Friesenhahn >> bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ >> GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ >> _______________________________________________ >> zfs-discuss mailing list >> zfs-discuss@opensolaris.org >> http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > > As someone who has spend enough time doing data center work, I can attest to > the fact that UPSes are really useful only as extremely-short-interval > solutions. A dozen or so minutes, at best. > > The best design I've see was for an old BBN (hey, remember them!) site just > outside of Cambridge, MA. It took in utility power, ran it through a > conditioner setup, and then through this nice switch thing. The switch took > three inputs: Utility, a local diesel generator, and a line of marine > batteries. The switch itself was internally redundant (which isn't hard to > do, it's 50's tech), so you could draw power from any (or even all 3 at > once). Nothing really fancy; it was simple, with no semiconductor stuff to > fail - just all 50-ish hardwired circuitry. I don't even think there was a > transistor in the whole shebang. Lots of capacitors, though. :-) > > > The jist of the whole thing was, that if utility power was out more than 5 > minutes, there was not good predictor of how long it would remain out - I > saw a nice little graph that showed no real good prediction of outage time > based on existing outage length (i.e. if the power has been out X minutes, > you can expect it to be restored in Y minutes...). I suspect it was > something like 20 years of accumulated data or so... > > The end of this is simple: UPSes should give you enough time to start the > gen-pack. If you are having problems with your gen-pack, you'll never have > enough UPS time to fix it (and, it's not cost-effective to try to make it > so), so FIX YOUR GEN PACK BEFORE the outage. Which means - TEST it, and > TEST it, and TEST it again!
Slight corollary -- just because you have a generator and test it doesn't mean you can assume you can get fuel in a timely manner (so still be prepared to shutdown if needed). I have seen places whose DR plans completely rely on the assumption there will never be any problems refueling their generators. However, last year after Ike hit, one of AT&T's central offices lost power because it ran out of fuel (and couldn't get refilled in time). > > > For home use, I set my UPS to immediately shut down anything attached to it > for /any/ service outage. Large enough batteries to handle anything more > than a couple of minutes are frankly a fire-hazard for the home, not to > mention a maintenance PITA. > > -- > Erik Trimble > Java System Support > Mailstop: usca22-123 > Phone: x17195 > Santa Clara, CA > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
