Power efficiency metrics - clearing up the thoughts
Wednesday Mar 21, 2007
Yesterday I posted about the power metric you should be using watt/performance, this fits with $/performance metrics you are familiar with. Performance has to be in the denominator. Watts cost money so it should be on top. Notice if you have 2.3 watts/performance another system that draws 4.6 watts/performance will end up costing twice as much.
OK, I told you that I was tired when I wrote the last entry, I got a little sloppy. The careful reader would notice that my metric is a bit off. watt/performance is a quick and good heuristic for comparison. But...
To have a proper metric the careful reader would have noticed that on your electric bill you don't buy watts, one buys kilowatt-hours (or watt-hours). Then to really perfect a power efficiency metric for datacenters one needs to change the denominator to highlight the focus on performance or work completed. If you are buying for performance(ops/sec) or work-done(ops) then you need to put this in the denominator.
Which bring us to:
Metrics:
Performance: watt-hour/(ops/sec)
Work: watt-hour/ops
... or kWhr/k-ops/sec or kWhr/m-ops/sec to scale it correctly.
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Posted by Pavel Anni on March 22, 2007 at 09:02 AM PDT #