Re: Monitoring for power outages on a dual-powered system

On 03/08/2010, at 9:56 AM, James H. H. Lampert wrote:

This is POSITIVELY THE LAST THING I WILL SAY ON THIS:

Me too.

1. In over sixteen years of experience with IBM midrange systems, I have
never, once, seen an internal power supply unit fail.

Good quality hardware--but if it weren't possible and hadn't happened in other installations why do you suppose redundant power supplies are included as an option? Oh, of course, so you can plug them into separate power sources ... silly me.

On the other hand,
A. I have seen line power fail multiple times

True. That's why people install UPSes and generators.

B. I have seen UPSs from two different manufacturers fail with
absolutely no advance warning whatsoever
C. I have seen UPSs send "On Battery Power - battery nearly dead"
messages through the monitoring cables, during self-tests, on more than
one occasion, when there wasn't a damned thing wrong with the line power.

I'd say poor quality UPS, or poor quality cables, connectors, or some such, or a UPS not designed for the attached hardware.

2. If, as you say, multiple redundant power supplies were not intended
to be plugged into separate power sources to guard against one of the
sources going down, THERE WOULD BE NO REASON FOR TWO SEPARATE AC CORDS.

If you believe two power cords indicates you should use two separate power sources then nothing will convince you that what you're doing, while perhaps not wrong, is at least short-sighted. So go for it. You've been told of the consequences--if you think your approach is better then why should we waste effort explaining otherwise.

The question is about monitoring for one or the other power source
cutting out at a time when nobody is here to notice, NOT monitoring the
UPS itself (which we do NOT do, PRECISELY because item 1C has occurred
on multiple occasions).

Which again points to a poor quality UPS. A good UPS will send the correct signals which is why you monitor for UPS status messages and engineer an orderly shut-down when no one is present to notice. As has already been pointed out the system hardware will monitor the failure of a power supply. But again you know better so have fun monitoring for that and let us know how it works out for you.

Regards,
Simon Coulter.
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