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

[Simon Coulter <shc@xxxxxxxxxxxxxxxxx>]

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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