One thing people seam to have forgotten is that with added redundancy comes added complexity that is many cases out ways the gain. Shaun

-----Original Message----- From: Alex Rubenstein [mailto:alex@nac.net] Sent: Thursday, May 29, 2003 1:40 PM To: Sean Donelan Cc: nanog@merit.edu Subject: Re: "They all suck!" Re: UPS failure modes (was: fire at NAC)

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UPSes (and UPS batteries) do fail, sometimes in catastrophic ways. I would not design any critical system on the assumption that any particular component won't fail. High availability is about designing for failure. Sometimes there is a long time between failures, other times they occur early and often. The most annoying thing about UPSes is they fail at exactly the time they are needed most.

Except, that:

Even in instances where 'High availability' is designed, in the case where one of the units has a failure that causes a fire and FM200 dump, either the FM200 will still trigger an EPO, or the fire department will.

So, the second 'high available' unit will generally not prevent you from dropping the critical load, but instead, will help you get back on line quicker.

A much cheaper and easier to implement external maintenance make-before-break bypass will accomplish the same thing.

I've heard many a story of the paralleling gear causing the problem in the first place, as well...

-- Alex Rubenstein, AR97, K2AHR, alex@nac.net, latency, Al Reuben -- -- Net Access Corporation, 800-NET-ME-36, http://www.nac.net --