Path: utzoo!attcan!uunet!comix!jeffl
From: jeffl@comix.UUCP (Jeff Liebermann)
Newsgroups: comp.unix.sysv386
Subject: Re: Cheap or free auto-shutdown setup (was: Reliability Sys V file sys)
Summary: UPS doesn't fix everything
Message-ID: <80@comix.UUCP>
Date: 4 Oct 90 08:52:23 GMT
References: <1990Sep29.220137.6550@intek01.uucp-> <1030@bilver.UUCP> <257@bongo.UUCP>
Organization: COmmittee to Maintain Independent Xenix
Lines: 65

> having one. But invoking shutdown, will still leave the system sitting 
> there waiting for either a human to turn off the machine or the UPS 
> power to die and cause havoc to the file system. Remember the purpose 
> of this excercise is to prevent instant power loss damage.
> 
> 1.	Identify a power outage
> 2.	Start shutdown
> 3.	Abort shutdown, or reboot if power returns within a specified period.
> 4.	Switch off machine after shutdown is successful
> 5.	Switch machine back on after power has been restored for a certain 
> length of time.

Close.  I think most users have a rather odd illusion that the UPS is
a generic fix for most AC power related problems.  The implimentations
for shutdown previously mentioned only work under ideal conditions.
Last year, Santa Cruz survived an earthquake.  We learned a few new
lessons about computer reliability.  My conclusion is that the UPS
is only useful for MINOR power line disturbances.

1.  The power died about 20 seconds after the quake started.  During
these 15 seconds, the power was there but oscillating wildly.  Most
UPS's did NOT activate during this time.  The high frequency trash
went straight thru the UPS, filters, surge protectors, switching
power supplies, and ended up causing 2 hard disk controller cards to
lose step and eat the data on the hard disk.

2.  Two customers were in the middle of an automatic backup during
the quake.  In one case, the UPS kept the system up long enough to
complete the backup sucessfully only to have the computer, tape, and
UPS flooded with rusty water from the overhead sprinklers.  In the
2nd case, the hard disk bounced around so much, that both the
drives and the backup tape were garbage.

3.  Two other customers wished they didn't have UPS's.  The UPS
kept the drive running for about 30 minutes after the start of the
quake.  The shaking didn't stop for 5 MONTHS and we had regular
aftershocks.  The hard disks were literally pounded into uselessness
in the first few minutes.

4.  Swaying power lines were a real problem.  One area had a 15Kv
distribution line touch the local power line.  Everything turned on
and plugged in was vaporized.  The power was also erratic for weeks.
The problem wasn't when the power dropped off, but when it came back
on.  It usually appeared as a major hi-voltage spike.  MOV (metal-
oxide-varistor) type of surge protectors couldn't handle the energy
and either exploded or caught fire.   I lost 2 UPS's, 3 surge
protectors, and one computer this way.

These stories are only the ones related to UPS's.  My current opinion
is that what I really want is about 1 second of power "float" from
a large capacitor to take care of the transients.  The hard disk
should have a good brake on the spindle.  Longer than about 1 sec.
and the power to the computer drops IMMEDIATELY and stays off until
the power is absolutely stable for 10 minutes.  I care less about
trashed data, files, and such than a $$$$$ hole in my budget.  Any
of the previously mentioned "graceful" shutdown scripts will take
far too long to bring the system down before a quake, or the
power company take their toll.


-- 
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