We have a number of SuperMicro RAID 10 boxes with redundant PSU, the same model and spec and use the same rackmount APC UPS. One has suddenly taken to rebooting if there is a minor brown-out.

Windows logs only point to 'unexpected' - as in loss of power. This has happened before and replacing the UPS has always fixed it. So we swapped out the 4 year old UPS for a new one. As the server was booting the UPS decided to self-test, and the server rebooted again!

We couldn't fault the unit we took out, so unless two PSU's are playing up at the same time I can't think of anything else that could cause it. Swapping out the standard UPS for an online one would almost certainly cure it, but if something is failing...

============= FURTHER CLARIFICATION OF QUESTION =======================

  1. The server has stayed up for nearly four years using the same UPS and configuration

  2. Recently any drop in utility power (that causes the UPS to switch to battery) and the server reboots.

  3. Swapping out the UPS does not appear to have fixed the issue as it went into self-test when the server was booting and it (the server) then rebooted.

I assume there is a controller for the PSU's? Something has become more sensitive to the milliseconds it takes to switch in the last couple of months.

With downtime being a major factor replacing the UPS again with an online one (like the APC SRT range) would cure the current problem - but is this a symptom that could develop into another serious issue?


IPMI event log

  • "so unless two PSU's are playing up at the same time" - and both connected to the same UPS? You are aware how much standard practices are violated with this? What does the APC log say? – TomTom Mar 26 at 21:43
  • We don't use Powerchute but the log from the extended menu on the unit shows nothing – gchq Mar 26 at 22:20

edit: You are having one of three problems which you cant verify without more logging of the length of outage that the system is losing power on. You did mention seeing transient losses on the UPS You need to correlate those with the logs from the Supermicro. If you dont want to use the UPS logs, you can instead attach one cord to the wall, but the UPS log will provide much better detail on the state.

All of these would trigger the Bios event log to record a power loss event. (1) The actual problem outage is longer, (2)The UPS is not providing the power needed during the transient(regulation issue), or (3)there is a problem with the PSU's or the PDU in the system not maintaining Power Good(PG) state to the motherboard.

Supermicro chassis draw different amounts of power depending on how many psu are operating. A dual psu system is drawing 50% load from each psu when the ups goes low, the lagging supply attempts to go 100% and accelerates the ups draw-down.

You shouldn't have both supplies in the SAME ups, and you should be looking at your ups load via management.

YOU SHOULD also be aware that the ups loads will double on the non-browning ups. My guess is the UPS is not sized properly to the peak load expected. That is affecting the systems and the UPS.

The information from the management GUI on the UPS contains graphs about power quality as well as battery status and load information. This will tell you if you're brownouts are happening at particular times and let you maybe track down the reason why you're having them in the first place.

The supplies do appear to be operating correctly when the power is good. Unknown as yet is what happens when the issue happens. The removable internal PSU's only put out +12 volts and PowerGood(+5). Internal to the system is a Power distribution Unit (PDU) unit that has the cords onto the motherboard and splits the +12v into all of the other voltages that the motherboard needs. When the UPS has the transient, for whatever reason the power to the Supermicro is falling outside the ATX spec(below) and the system is shutting down. That is at 95% of rated values.

It is possible for that PDU to be bad, but the only way to test it is by swapping the supplies from a system not seeing the problem. Swapping the PDU is a real chore.

Per the ATX specification: The ATX specification requires that the power-good signal ("PWR_OK") go high no sooner than 100 ms after the power rails have stabilized, and remain high for 16 ms after loss of AC power, and fall (to less than 0.4 V) at least 1 ms before the power rails fall out of specification (to 95% of their nominal value). Wikipedia ATX Power good

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  • The main reason for using the same UPS is (apart from lack of space in the rack) to cover the PSU's. It's worked flawlessly for years and powered the unit for some 20 mins during compete power outages - as with the other identical server/UPS configurations. Brown-out may have been the wrong term, it's a very short drop in utility power. The drop is so short that, for example, clocks on things like the toaster oven that will reset if the drop is longer than a second or two are not effected, but a fish tank pump has to be re-primed if it's a split-second drop. – gchq Mar 28 at 1:12
  • UPS is running at 11% load. I would not have thought that to be excessive. It's giving itself a clean bill of health during a self-test (both the old unit and replacement), but the server is rebooting during the switch to battery - something it's not done in the past. – gchq Mar 28 at 1:18
  • You are correct, 11% is not much loading on the ups. The term for those types of drops are transients. Without logging from the ups, you don't kbow how often they are occurring, you only know when there is a full cut. The UPS log would also let you have something to go back to your power supplier because transient should not happen that often. You can also monitor the psu's in the Supermicro over the management interface from another system with Ipmicfg. It doesn't matter if ipmicfg is running on Windows or Linux for that to work, you just need to pass it ipmi credentials preferably by file. – Rowan Hawkins Mar 28 at 22:23
  • What may work better is SuperDoctor 5 which is free from supermicro and will let you log information better than dumping it to a file. I misremembered the commands for ipmicfg and they were actually for an older version SuperDoctorII which I ran from command line on linux. – Rowan Hawkins Mar 28 at 22:40
  • Rowan - I did, recently, install SuperDoctor. I didn't install the web browser part though, so might have to go back and reinstall. It's currently running something with Java. There is a SuperMicro BMC utility that gives both PSU's a clean bill of health - along with everything else. So far there have been three drops and one self test this year. – gchq Mar 29 at 1:13

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