by Johan De Gelas
Performance per Watt rules the datacenter, right? Wrong. Yes, you would easily be lead astray after the endless “Green ICT” conferences, the many power limited datacenters, and the flood of new technologies that all have the “Performance/Watt” stamp. But if performance per Watt is all that counts, we would be all be running atom and ARM based servers. Some people do promote Atom based servers, but outside niche markets we don’t think it will be a huge success. Why not? Think about it: what is the ultimate goal of a datacenter? The answer is of course the same as for the enterprise as a whole: serve as many (internal or external) customers as possible with the lowest response time at the lowest cost.
So what really matters? Attaining a certain level of performance. At that point you want the lowest power consumption possible, but first you want to attain the level of performance where your customers are satisfied. So it is power efficiency at a certain performance level that you are after, not the best performance/Watt ratio. Twenty times lower power for 5 times lower performance might seem an excellent choice from the performance/watt point of view, but if your customers get frustrated with the high response times they will quit. Case closed. And customers are easily frustrated. “Would users prefer 10 search results in 0.4 seconds or 25 results in 0.9 seconds?”
