To sketch the situation :
- a bunch of servers (~15 going from 4u to 1u, some redudant PSU some single)
- 2 UPS (1 APC I can read using apcupsd)
- 2 PDU
So I came upon this situation, and I honestly have no idea what the best solution would be. We have currently put most of the servers (even redundant PSU) on 1 UPS (older one, no APC) Then when we started drawing too much juice from it, it started to complain and they bought another one, and changed the probably most power hungry servers (clusters) on the new UPS (APC)
I don't mind servers going offline during a power break, and I would like them to go down well before the UPS give out. Currently the servers run until they don't get any more power, then die painfully.
So the reasonable situation would be that we dedup the servers who can so that they pull 50/50 from each UPS (as far as possible). However, during a power down, one of the batteries would be finished before the other one, this would result that ALL the servers draw juice from the other UPS, probably pulling way to much power and resulting in a instant power break?
So my questions are do PSU pull 50% from each power source? And how can I (if necessary with new hardware) fix this situation. And what is the worst that can happen when you pull too much from a UPS ?
I want to protect the servers from high peaks in power and in short outages of <5 min. Anything beyond this time-frame is explainable up the ladder. Or servers are configured OK and we know they can power cycle if deemed necessary.