UPS backup musings

[covici at ccs.covici.com]

My ups does neither of those things -- power fails, ups stays on till I
shut everything off, or battery runs out.  So for those one second
outages, it works great machines never go down at all.

Gregory Nowak <greg at gregn.net> wrote:

> Hi all,
> this is primarily aimed at those here who have UPS (uninterruptable
> power supply) battery backup units. I seem to recall Kirk has one, and
> maybe others here do as well.
> 
> We have a power outage here every 3-4 months, lasting anywhere from
> one second to close to 3 hours so far. So, I had been thinking of
> getting a UPS some day for a while now. According to my
> server/router's uptime, our most recent outage happened 36 days ago,
> and it lasted for a second, if not less. Everything including clock
> radios and stove clock seems to have survived it, except for the
> server. The fans and drive stayed on, but the machine was
> unresponsive, forcing me to power cycle it. That's when I decided that
> this happens frequently enough, and is annoying enough to maybe turn
> some day into in the near future.
> 
> Until I researched UPS units, my idea of how they work was perhaps too
> idealistic. Power fails. Server properly shuts down. Power comes back
> on, server starts up. I found out though that this doesn't seem to be
> exactly how things go though.
> 
> My server is setup in bios to turn on whenever power is applied. My
> research seems to indicate that there are two extremes as far as UPS
> units go. In the first extreme, power fails, the server shuts
> down. However, since the UPS isn't fully drained, the power from the
> UPS stays on, and the server doesn't start back up when the power
> company gets their act together, and utility power comes back
> on. That's fine if someone is around to press the power
> button. However, what if when this happens everyone here happens to be
> on a longer vacation?
> 
> In the second extreme, some UPS units are set to cut power, and
> reapply power again about a minute after utility power comes back
> on. If the server shuts down before utility power comes back on,
> that's good. If utility power comes back on before the server shuts
> down, then the UPS causes the very problem it is supposed to
> prevent. This leads me to conclude that they're worth getting if one
> has a backup generator, or power outages tend to be short, and the UPS
> unit doesn't cycle the power.
> 
> I also question the value of a proper shut down these days. Before
> journaling file systems, an improper shut down was a headache. Now
> though, it doesn't seem to be such a big deal. I've been through power
> failures maybe ten times now, and every time so far, the journals were
> recovered, and the system fully booted up, and was ready for prime
> time without my intervention (except in cases of split second
> outages). On the other hand, when we were having some electrical work
> done recently, I asked the electrician to wait for me to shut down
> the server before he cut the power, instead of just letting him cut
> power whenever he was ready.
> 
> To keep this somewhat on topic, since the server only has USB ports,
> and no serial port, I was concerned about the compatibility of USB UPS
> units with gnu/linux. Based on reviews, the unit I would get if I
> decide to get it seems to be compatible with gnu/linux using USB to
> communicate:
> 
> http://www.newegg.com/Product/Product.aspx?Item=N82E16842101311
> 
> Finally, though not strictly necessary, I can't help thinking that it
> would be nice to power my dsl modem, network switch, wifi access
> point, server, and maybe charge other battery devices during a power
> outage for a while. I'm also wondering how hard it is to find
> replacement batteries locally or on-line? While I see UPS battery
> backup units on newegg, I haven't yet found a category with
> replacement batteries for them. The reviews seem to indicate that new
> batteries run for about $30 U.S., so that isn't bad, if I only knew
> I'd be able to find them in order to buy them.
> 
> So for those of you who have these units, are they worth it, or are
> they maybe less valuable to have than in the past? Thanks for any
> comments.
> 
> Greg
> 
> 
> -- 
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> 
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-- 
Your life is like a penny.  You're going to lose it.  The question is:
How do
you spend it?

         John Covici
         covici at ccs.covici.com