UPS backup musings

[Gregory Nowak]

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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