On Wed, Dec 18, 2019 at 10:48 AM Thomas Bellman <bell...@nsc.liu.se> wrote:
> On 2019-12-18 15:57, Rod Beck wrote: > > > This led me to wonder what is the inefficiency of these servers in data> > centers. Every time I am in a data center I am impressed by how much> heat > comes off these semiconductor chips. Looks to me may be 60% of the> > electricity ends up as heat. > What are you expecting the remaining 40% of the electricity ends up as? > > There is another efficiency number that many datacenters look at, which > is PUE, Power Usage Effectiveness. That is a measure of the total energy > used by the DC compared to the energy used for "IT load". The differece > being in cooling/ventilation, UPS:es, lighting, and similar stuff. > However, there are several deficiencies with this metric, for example: > > - IT load is just watts (or joules) pushed into your servers, and does > not account for if you are using old, inefficient Cray 1 machines or > modern AMD EPYC / Intel Skylake PCs. > > - Replace fans in servers with larger, more efficient fans in the rack > doors, and the IT load decreases while the DC "losses" increase, > leading to higher (worse) PUE, even though you might have lowered your > total energy usage. > > - Get your cooling water as district cooling instead of running your own > chillers, and you are no longer using electricity for the chillers, > improving your PUE. There are still chillers run, using energy, but > that energy does not show up on your DC's electricity bill... > > This doesn't mean that the PUE value is *entirely* worthless. It did > help in putting efficiency into focus. There used to be datacenters > that had PUE numbers close to, or even over, 2.0, due to having horribly > inefficient cooling systems, UPS:es and so on. But once you get down > to the 1.2-1.3 range or below, you really need to look at the details > of *how* the DC achieved the PUE number; a single number doesn't capture > the nuances. > Google has some information on PUE at https://www.google.com/about/datacenters/efficiency/ -- the tl;dr is that we have a datacenter PUE of 1.06, and a campus (including power substation) PUE of 1.11. By comparison, most large datacenters average around 1.67. Damian