Power consumption -- real vs actual

John LLOYD jal at mdacorporation.com
Mon Apr 5 11:37:45 CDT 2010

We're coming up against power consumption issues on some servers, usually 10g (r900) and 11g (r710,r610) boxes.

I'll use an R710 as an example.

The nameplate rating, used for electrical safety, is 7 amps for an R710 (100V to 120V).

The power supply rated capacity is 870W (for the high-output version).

The enterprise power calculator dell.com/calc  says input power is 431 watts, maximum 578 watts.

Open Manage reports power consumption (at idle) is 252W.

Now, with this surplus of numbers to choose from, I have a few concerns.  

First, the enterprise calculator shows maximum (578) less than power supply capacity (870) which is a good thing.

But, second, the power supply capacity is more than rated input which is 7A * 100V=700VA.  What is the basis for the current rating on the nameplate?

(By nameplate I mean the black decal with numerous regulatory logos, input voltage/current ratings, model numbers, etc.)

Third, while idle power is less than calculated (and I do understand why), why so much less?  Try as I might, I cannot get my 252W reported by OpenManage up near the 431W calculated, by exercising CPUs or disks.  So, does OpenManage report "input" power or "output" from the power supply, or, something else?  Or is the calculator based on highest-expected values rather than averages?

Fourth, the Open Manage mechanism to measure power is based on whatever is built into the chassis.  How accurate (% of actual) could we expect this to be?  5% or 20%?  And is it "input" to the power supply or "input" to the baseboard?

FYI, commands were
 CPU heater:  dd if=/dev/zero of=/dev/null  &    8 to 16 times
 disk heater:  tar cf /dev/zero /path/to/big/disks/as/raid-5
 measure power:  omreport chassis pwrmonitoring | grep Reading | head -1
Config is
# SPident
CONCLUSION: System is up-to-date!
  found    SLE-10-x86_64-SP2 + "online updates"
Hardware is R710, two Intel(R) Xeon(R) CPU X5570  @ 2.93GHz, (quad-core)
Six 600GB SAS disks.  One Perc 6/I controller.
Open Manage is 6.1


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