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

In 13 years at my present employer, we did have a power supply failure. It was a 620 with one supply. The CE had not seen one fail. A replacement took almost ten hours to arrive, and then there was the rebuilding of access paths. I do not recall if dual power supplies was an option on that 620, or whether somebody thought the second supply was too expensive. The real expense of a downed system for nearly 24 hours had to be more than a second supply. Even replacing the thing on the 620 was time consuming. Back in the 90s, I recall a sales pitch about EMC disk modules. They had THREE supplies. Two were required to run the unit.

John McKee


-----Original message-----
From: "James H. H. Lampert" jamesl@xxxxxxxxxxxxxxxxx
Date: Mon, 02 Aug 2010 18:56:00 -0500
To: Midrange Systems Technical Discussion midrange-l@xxxxxxxxxxxx
Subject: Re: Monitoring for power outages on a dual-powered system

Simon Coulter wrote:

Of course there is. Redundant power supply units are to protect
against failure of one power supply unit.

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

1. In over sixteen years of experience with IBM midrange systems, I have
never, once, seen an internal power supply unit fail. On the other hand,
A. I have seen line power fail multiple times
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.

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.

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).

--
JHHL
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