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I have a giant 24u server (Supermicro 4U X9DRI-F w/ 2x Xeon E5-2680) with 2 1200w PSUs. However, I only have 4 drives in right now, and my actual power draw (under the most stressful loads) is likely not more than 500w.

I have these PSUs plugged in to one 1800J/20A UPS. I (naively) figured this would be more than enough since I don't draw anywhere near the total load my server can pull (except, as I discovered, during startup).

I had thought that my OS (unRaid) deliberately kept HDDs offline so as to avoid power spiking on startup, but I think maybe the initial boot is outside its control.

When I boot, my UPS beeps for a while, telling me I'm overloading it. Once the OS boots, the UPS calms down and hums along fine. Even when the HDDs are switched on, it's fine.

So, is there anything in (maybe) the BIOS I can do to set the PSUs to draw less max power? Or would a solution be to get a second UPS and have the 2nd PSU plug in to that?

Mike Manfrin
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    The purpose of dual PSUs is usually redundancy. So yes, you should have both PSUs plugged in to separate mains / UPSes, so a failure on one will not bring the server down. – Appleoddity Sep 09 '18 at 06:28
  • The only thing you can affect in startup power is *disk staggered spinup* on the RAID controller. Also, I'd go with either Appleoddity or Ian to use separate power sources. – Zac67 Sep 09 '18 at 08:40
  • What is the actual draw at start measured when plugged into a power meter? "Full load of both PSUs" implies 2000 W, you estimated 500 W. – John Mahowald Sep 09 '18 at 15:58

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A third option is to plug one PSU into a surge protector and then into the wall, since you only need 1 to safely shut the server down when the power goes out.

Ian Marshall
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