Did you know that Google designs their ultra-power-efficient data centers to operate between about 32% and 42% of max processor speed? That is, between Breguet Number (“max fuel economy”) and Carson’s Speed (“the least wasteful way of wasting” power greater than the Bruequet Number).
If you have wondered how Google manages to not only keep up with the exponential growth of the Internet, but to continuously add new compute-intensive features (like Instant Search), this is for you. I think Bob Cringely is one of the best tech-industry writers — this piece on Google’s data centers is an example of Bob’s best. BTW, Cringely is a pilot. Excerpts:
(…) A couple years ago the company did research to figure out at what processor performance level — at what percentage of CPU capacity — data center power consumption was minimized. No other company but Google would consider a strategy of deliberately throttling-back its data centers.
Whether Google even realized it this approach to transport efficiency has been around for a long time… in aviation. What Google separately sought were two very special data center power levels known in aeronautical engineering as the Breguet Number and Carson’s Speed.
(…) This brings us to Carson’s Speed. Bruguet was a French engineer best-known for his family’s fine watches, while Carson was a professor at the U. S. Naval Academy.
The problem with Breguet Numbers for pilots is that airplanes are intended to go fast and Breguet-friendly power levels are slow and boring. Going faster is a constant temptation with airplanes because they are of necessity built with a lot of excess power — power that is needed for climbing to altitude. An airplane built with an engine small enough to only reach Breguet Number speeds wouldn’t have enough power to even get off the ground. If you have excess power (and finite patience) what is the best speed to fly?
That would be Carson’s speed — the speed to get the most extra speed for the least extra cost. Or, as Carson put it, of finding “the least wasteful way of wasting.” For aircraft the speed in question turned out to be 1.32 times the speed for most miles per gallon (the Bruguet Number). Carson’s Speed uses excess power most efficiently.
Other than three G-V’s and one Boeing 767 built for a harem, Google flies data centers, not airplanes. But Google’s situation going into its power experiment was actually very similar to aviation because it was an exercise in reducing power. Google data centers weren’t built to Bruguet specs, they were faster. Given this excess computing power that had already been paid for in capital terms, what was the most efficient way of using it? Carson’s Speed — about 43 percent power — leaving plenty of excess cycles for new services like Instant Search.
But once you enable Instant Search for everyone, the data center is again running consistently above its Carson’s Speed which means you need even more hardware to bring the building back to 43 percent. It’s an arms race that until this moment only Google may have known they were conducting.