UPS - single points of failure

[Rich Braun]

(This is a resubmission, the first one went into the BLU void.  My comments
remain unchanged four days later.)

Date:  	Mon, November 27, 2006 10:54 am
To:   	discuss at blu.org

As I prepared Thanksgiving dinner, the UPS on my file server abruptly gave up
the ghost after a few years of service.  I'm obsessed with fault tolerance and
power efficiency, so the "Uninterruptable" Power Supply has always been a bit
of a sore topic for me.

(This is a bit long, executive summary is:  consider Xantrex Powersource 400
because it provides long runtime, 10 times longer than rivals.)

In the past 10 years, I've seen the quality of hard drives increase to the
point where they are more reliable than UPS units.  (When was the last time
you had a hard drive die?)  Yet consumers still buy hard drives--a product of
high complexity--with the expectation that they'll inevitably fail someday.
Consumers buy UPS units--fairly simple products, by comparison--with the
expectation that they should never fail, at least until the batteries give
out.  For some reason, the marketplace has not led to the reliability
improvements one would expect in UPS units.  A decade ago, I recall that many
of the customer-visible outages at the ISPs I helped to manage were caused by
failed UPS units.  Problems persist today.

APC still has the bulk of the market for consumer UPS units.  I absolutely
*hate* that brand, at least in the consumer category.  So when my Tripp-Lite
failed, I sought anything but APC.

I'm writing this because I stumbled into a unit that, if it proves reliable,
is a surprisingly good deal versus the consumer-grade competition.  At my
house, power outages are relatively uncommon.  There are maybe 10 brief (less
than 10-second) interruptions annually, and maybe 1 or two lengthy (1- to
5-hour) annually.  Interruptions of 10 seconds to 3600 seconds almost *never*
happen (maybe once or twice a decade), and I haven't seen a super-long one
(6-hour plus).  Hence for me the typical runtime spec of a UPS unit is
inappropriate to my needs.  A minute or two of runtime is enough avoid crashes
during short interruptions and/or to save my work; 20 or 30 minutes of runtime
isn't going to last through a typical long outage, and isn't worth paying
extra for.

There's a manufacturer of renewable-energy products which has come out with a
UPS that seems to fit my needs just fine.  I got a couple of these units
(Xantrex 400) at Best Buy this weekend, after comparing online prices and
Microcenter (they have the brand but none in stock, at a price higher than
Best Buy).  Last night I ran a runtime test.  Get this--my file server ran 6
hours 55 minutes before the unit shut down!

My VIA-based server with 2x300Gb storage only consumes 48 watts but this
implies that even a 100-watt server could run for over 3 hours, thanks to the
big honkin' batteries inside (480 volt-amp-hours' worth.) If you had to buy
the batteries separately, you'd pay about $120--this UPS sells for not a whole
lot more than the batteries alone.

On the efficiency side, the annual operating cost of a UPS here in New England
is about $1.75 times the wattage differential between input and output.  My
old Tripp-Lite ate about 11 watts along the way from the wall to the server.
The Xantrex uses about 5 watts.  So I'm also saving about $10/year with this
unit installed.

Why am I writing this review here for the BLU group as a suggestion for
consumer (versus data center) installation?  Because in a data center you'd
probably want to have the UPS units connected to monitoring software.  Even
the cheap consumer grade UPS units usually have a USB or serial port.  Xantech
omitted this essential ingredient.  Were I to design this thing, I'd leave out
the silly LED panel display and include USB, which would probably reduce build
cost anyway.

Your mileage may vary, and I might ultimately be an unhappy camper if this
product turns out to be an unreliable turkey.  But I'm very happy to see long
runtime arriving in a consumer UPS product (given that these products, and PC
power supplies, are promoted mainly with useless/misleading wattage figures
designed to appeal to adolescents seeking "more power").  Might be worth
contemplating for your own Linux setup.

Now, someday maybe the power supply manufacturers will come up with a way to
make consumer-priced PCs without a single-point-of-failure on the power input.
I guess that'll be the day when Microsoft includes software RAID1 in their
"Home Edition" O/S. ;-)

-rich


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