Bob Friesenhahn wrote:
On Tue, 30 Jun 2009, Neal Pollack wrote:
Actually, they do quite a bit more than that. They create jobs,
generate revenue for battery manufacturers, and tech's that change
batteries and do PM maintenance on the large units. Let's not
It sounds like this is a responsibility which should be moved to the
US federal goverment since UPSs create jobs.
Actually, I think UPS already employs some 410,000+ people, making it
the 3rd largest private employer in the USA. (5th overall, if you
include the Federal Gov't and the US Postal Service).
<wink>
In the last 28 years of doing this stuff, I've found a few times that
the UPS has actually worked and lasted as long as the outage.
I have seen UPSs help quite a lot for short glitches lasting seconds,
or a minute. Otherwise the outage is usually longer than the UPSs can
stay up since the problem required human attention.
A standby generator is needed for any long outages.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us,
http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
As someone who has spend enough time doing data center work, I can
attest to the fact that UPSes are really useful only as
extremely-short-interval solutions. A dozen or so minutes, at best.
The best design I've see was for an old BBN (hey, remember them!) site
just outside of Cambridge, MA. It took in utility power, ran it through
a conditioner setup, and then through this nice switch thing. The
switch took three inputs: Utility, a local diesel generator, and a line
of marine batteries. The switch itself was internally redundant (which
isn't hard to do, it's 50's tech), so you could draw power from any (or
even all 3 at once). Nothing really fancy; it was simple, with no
semiconductor stuff to fail - just all 50-ish hardwired circuitry. I
don't even think there was a transistor in the whole shebang. Lots of
capacitors, though. :-)
The jist of the whole thing was, that if utility power was out more than
5 minutes, there was not good predictor of how long it would remain out
- I saw a nice little graph that showed no real good prediction of
outage time based on existing outage length (i.e. if the power has been
out X minutes, you can expect it to be restored in Y minutes...). I
suspect it was something like 20 years of accumulated data or so...
The end of this is simple: UPSes should give you enough time to start
the gen-pack. If you are having problems with your gen-pack, you'll
never have enough UPS time to fix it (and, it's not cost-effective to
try to make it so), so FIX YOUR GEN PACK BEFORE the outage. Which means
- TEST it, and TEST it, and TEST it again!
For home use, I set my UPS to immediately shut down anything attached to
it for /any/ service outage. Large enough batteries to handle anything
more than a couple of minutes are frankly a fire-hazard for the home,
not to mention a maintenance PITA.
--
Erik Trimble
Java System Support
Mailstop: usca22-123
Phone: x17195
Santa Clara, CA
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
