On Tue, Feb 10, 2009 at 12:40 PM, Jim McAtee <[email protected]> wrote: > So you purchase two of the same UPS, maintain them as best you can, then the > day > comes when you lose power and _one_ of them fails, what are the chances that > the other will hold up all of your servers?
Well, assuming they're not overloaded like they were for us, things should keep running. I apparently overestimated the amount of margin I had on our UPSes. If I had properly spec'ed things, the servers would indeed have kept running, despite the suicide of one of the UPSes. If I had load tested the configuration after some additional equipment was added, I would have seen the problem before it became critical. This was really due to oversight on my part. I was all too willing to believe a number in a management screen, when I should have done real testing. Fundamentally, my problem was a UPS that was overloaded when on battery but squeaking by on-line. That problem can happen with a single UPS just as much. Indeed, I've seen single UPSes buckle when they transfer to battery before, too. The problem of equipment bought at the same time going bad at the same time is a real one. I've seen that across any number of product categories: Hard disks, printers, whole computers. But if that invalidated redundancy, we wouldn't bother with RAID, dual PSUs, etc. There's a cost argument, to be sure. But I'm basically looking at it this way: For a given runtime, I could use one big UPS, or two smaller UPSes in parallel. With one big UPS, a UPS fault means everything dies. With two smaller ones, a UPS fault simply means runtime is reduced. -- Ben ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~
