Re: UPS comments?
From: Brian (brian_at_beepbeep.invalid)
Date: 02/04/05
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Date: Fri, 04 Feb 2005 00:37:13 +0000
On Thu, 03 Feb 2005 22:35:51 +0000, ac wrote:
> Are you using it in a business or home environment - reason for the
> question is that UPS's seem to be slightly rarely used, and I wonder if
> my objectives are realistic - for a small business/home use?
>
Well, you'll know what the answer is when you have that rare power cut
which not only looses your work, but trashes the disk too... :(
Mine is being used on the server of a home-based network, although I may
get another smaller one to allow graceful shutdown of the couple of
workstations I generally work with.
Ideally, I suppose, a UPS /should/ only be rarely required (if ever) but I
feel more comfortable for having one - the last power cut here (the first
in around 18 months) caused me to break out in a cold sweat as I dealt
with a string of disk-related errors when the server came back up.
I definitely don't want to go there again...
I've also been involved in a business environment where almost anything
resembling a server or machine which held important data had its attendant
UPS - if the data reconstruction after corruption would cost 10s of
thousands, what's £100 or so to ensure it won't happen?
> Also I note the bottom end model (eg SU420INET) only has a serial
> connection for control. I have seen a comment that such a connection is
> problematic and a usb connection was recommended - in a linux context
>
KISS (Keep It Simple, Stupid)
I was quite pleased to see the UPS I got had a serial port: serial is
nice because it can be poked and prodded using simple tools; the data can
be easily sniffed; it's trivial to write noddy programs to use it.
With USB things tend to get a little too "deep" for my preferred running
mode - instant results, and the abillity to play with easily it at a
hardware level if I want to.
If anything, I'd say that a USB device has the /capability/ of being more
problematic in that the correct kernel modules must be installed before it
can work, but good ol' serial ports are pretty much a rock-solid "given"
on any machine.
That said, if the daemon handling the UPS is happy with serial or USB as
installed from the RPM and all you want is the functionality, it's not an
issue. For the daemon I suggested, it's simply a case of telling it which
interface you've used, be it serial or USB. It's also clever enough to
check that the UPS is connected, and complain when it isn't.
> I would be very interested to know what you expect at mainsfailure -
> shut down or something before shutdown?
>
It can be set up in various ways, but my preferred is that when the mains
fails (and the UPS is now holding the server up), after a certain timeout
and if the mains hasn't since reappeared then the server is gracefully
shut down. It's as if you were at the console doing "shutdown -h now".
Later, after the shutdown, if the mains reappears then the server is fired
up automatically. Of course if the mains reappears before the timeout is
reached then the server just continues chugging away without a glitch.
And talking of glitches - for the past 3 months at around 2am the mains
supply here (20 miles north of London) drops to <190v for a few seconds,
then pops back up to 240v. That strikes me as being a low enough dip to
cause problems but having the UPS it's no problem at all. Mine is the
so-called Smart-UPS, so it reports all this interesting stuff. Ok, so I'm
easily amused too! ;)
Naturally all UPS activity gets logged and warning messages are broadcast
to any connected machines as the mains fails but that's of little
consequence in a domestic environment with a protected server feeding
unprotected workstations... ;)
Something you'd asked for earlier and I'd not commented on: you wanted all
open files to be neatly closed bfore the machine is shut down.
This may not be specifically possible - it really depends on how a
specific application behaves in response to being terminated. It might
try to cleanly close open files as it terminates, but I suspect the action
would be to just abandon ship as quickly as possible.
AFAIK there's no mechanism by which an application can be told by the OS
to save files and /then/ terminate - only that it should terminate. Happy
to be proved wrong here!
I think the main idea is that the equipment should be gracefully powered
off, but the applications are left to fend for themselves.
On a workstation though, it's something you can test quite easily. Set up
an application with an open and unsaved file, then at a console issue
"shutdown -h now" and see what's happened to the file when you restart.
B.
-- The idea is to die young as late as possible.
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