[rescue] SGI goodies anyone? - Power consumption..

Brian Deloria bdeloria at gmail.com
Mon Oct 18 12:13:20 CDT 2010

On Mon, Oct 18, 2010 at 12:02 PM, Robert Darlington
<rdarlington at gmail.com>wrote:

> Be careful with this assumption.  If the PSU is rated for 1500 watts,
> that's
> the max it will ever draw.  Most likely it will be much less unless you
> have
> every possible accessory jammed into every possible expansion slot.  I ran
> into this when specifying air conditioning systems for server rooms.  Using
> the label on the back of the computer or the printed spec in a data sheet
> means icing up chillers.  Typically I'm used to actual average power
> consumption in a server room being closer to *half* of all the printed
> ratings added up.

I'm used to seeing 30-40% of the actual rated power supply for most
'general' configurations.  i.e. standard cpu, not all the cards full, not
all 15k drives etc.  I don't know if they give access to this on Sun's
website anymore but you used to be able to calculate what the consumption of
power would be.  This was always nice and made it easier to size the ac, and
ups needs.  Some of the pc server manufacturers have calculators that you
can use to gather this as well.  I've still found that even with playing
around on some calculators, i.e. putting the hottest chips, 15k drives and
every card that can generate heat that it still doesn't usually get up past
60%.  On a side note I did have one machine that didn't have the fastest or
hottest chips and it was still running at 80% of the largest power supplies
for that system.  Loosely guessing at 30% of the rated power supply for a
rack of these would have caused a serious problem.

> That being said, your system might in fact pull that much power.   When
> you're running, try using an ammeter on the line powering them (split a
> power cable into individual conductors and clamp around either hot or
> neutral but not both because they cancel each other out).  I'd be very
> interested to see where these systems fall.

A short extension cord with exposed wires has done me wonders over the
years.  However, leave enough room so that you you want to you can loop the
wire multiple times through the ammeter.  If you find yourself between
measurement settings on there this can be helpful to double the number.

Just make sure you can see it for the initial spike when it powers on, it
can be a bit surprising.

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