We have a rack in a data center and we became suspicious of running out of power. But our power bar says 2 amps! It has a live indicator, so it's not just one reading. Do you think there's something wrong with the powerbar?

Worth mentioning: Until now we never checked the power bar to verify the numbers it said made sense.

Our equipment (approximately): Six 1U servers with 2 disks each. One 2U Dual Core with 6 drives One 2U Dual-Quad Core One MD1000 loaded with 15 drives Two other drive enclosures with 16 drives total.

We have many users and there's always activity, and if not, we're backing up. It's remotely possible that there was small amounts of activity of maybe 5 mbits/s, but 2 amps? That seems strangely low, but I'm not an electrician.

Why We Think We're Running Out of Power - Using general calculations or the Dell Capacity Planner (http://www.dell.com/html/us/products/rack_advisor_new/) we are at about 17-21 amps, which is the limit of our circuit.

  • We put 2 disks into a drive enclosure and our (completely unconnected) server on the power outlet next to the enclosure rebooted! There's no iSCSI or cabling between the 2 systems. This happened twice when we added disks on 2 different days. The server that rebooted is rock-solid. I've never seen it ever reboot unless we did it ourselves.

  • I've had experience with power issues in the past (different system entirely) and the same stuff that happened then is happening now.. Once every day or two, a server goes mostly offline for 30 minutes (pings but nothing else)... Random equipment strangeness (in this case, a drive enclosure is running really slow (could be regular performance but under 10 MBytesPS? We needed to move customers since it couldn't even deal with FTP traffic)... Again, I'm very open to the fact that this is due to other things, but it looks familiar to me.

  • 3
    Where is this gear located? In the U.S., voltage is delivered at different currents in many commercial/industrial applications than households. Typically 120/240 is found in residential, while 110/208 is delivered to commercial locations. Not that this helps solve your reading trouble, but it may help the accuracy of your calculations moving forward. – mcmeel Aug 10 '11 at 16:16
  • It's in a data center in Toronto, Canada. We use the same standards as the USA. (I'm pretty sure.) – Jay Aug 10 '11 at 17:16

Most 1U servers pull at least 300 watts, presumably you're in the states so that's;

Amps = Watts / Voltage

So 6 x 300 Watts divided by 120 volts equals 15 amps.

And that's a bare miniumum, you're probably pulling much more than that.

So basically your reading is way wrong.

  • Wow - I thought I was being generous, I know a lot of mine are WAY over 300w each, more like 600w in fact - hmmm...I'm not doing the planet much good now am I... – Chopper3 Aug 10 '11 at 16:00
  • I think that's pretty normal for loaded servers. Mine are pretty RAM bound at the moment; processors rarely do much. – Chris S Aug 10 '11 at 16:07
  • Data centers in the US frequently have 240V available. – wfaulk Aug 10 '11 at 17:17

If you're running on 240v, and it's rounding 2.49 down to 2, then you could be drawing almost 600W. That amount would make sense for 6-8 very power efficient servers; drives pull a couple watts each. It's within the realm of possibility, but I doubt it's accurate.

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