[2029] in SIPB-AFS-requests
Re: Power layout in machine room
daemon@ATHENA.MIT.EDU (Greg Hudson)
Mon Jun 12 16:11:22 1995
To: Jonathon Weiss <jweiss@MIT.EDU>
Cc: tom@MIT.EDU, rtfm-maintainers@MIT.EDU, sipb-afsreq@MIT.EDU
In-Reply-To: Your message of "Mon, 12 Jun 1995 15:33:23 EDT."
<199506121933.PAA08539@the-other-woman.MIT.EDU>
Date: Mon, 12 Jun 1995 16:10:35 EDT
From: Greg Hudson <ghudson@MIT.EDU>
Tom Coppeto and Jonathan have both suggested that we put the Maxines
on the UPSs. Jonathan wrote:
> Is there really a good reason to not put the maxines on a UPS when
> we put their disks on one? Putting them on a UPS would mean that we
> had some chance of not losing if there was a power hit. Maxines on
> these UPSs tend to lose when power comes back. This means that if
> there is an extended outage we might have a chance to bring them
> down cleanly.
My reasoning is as follows:
* Most power outages are very short, and we'd be unlikely to
actually be around and be able to cleanly power off machines
during a long outage. Further, unclean shutdowns are rarely
very harmful. So "possibility of bringing down services
cleanly" doesn't seem significant.
* My understanding of the UPS problem, from talking with Tom
Coppeto, is that new Maxines will tend to notice a change
when power cuts from the UPS power back to normal power, and
the Maxine will turn off and stay off. If this is common,
it means that the UPS will make it more likely for the
Maxine to stay down after a power glitch than if the Maxine
weren't on the UPS.
* Maxine power supplies sometimes do fail to turn back on
after a power glitch, but my observation is that it's pretty
uncommon.
* Putting Maxine disks on the UPS is fine, and will help
eliminate the possibility of Maxines coming up without their
disks after a power outage. I wasn't planning to cut the
disks over until the power outage on the 25th, or some other
convenient time.
If somebody informed can convince me that I'm wrong about this
argument (i.e. that the UPSs don't actually fail very often, so they
won't stay off after power outages very much, and it's better to have
them on the UPSs so that the machines will usually stay on during a
power glitch), then I will amend my mail to athena-outages and say
that there will be an AFS and RTFM outage next weekend as well.
