I read a very interesting article from fellow blogger Christian Belady, who is Principal Power and Cooling Architect at Microsoft.
Christian decided to take the PUE challenge and see if he could build a data center with a PUE of one! That is to have all of the power delivered to computing equipment and none at all “wasted” on power protection and cooling. Most data centers have a PUE of between 1.2 and 3, with 1.2 being very good and 3 being the SUV model. Christian writes:
What would a data center look like with a PUE of 1.0? A PUE of 1.0 essentially means that all the power consumed in the data center generates compute operations and there is no additional cooling or power overhead.
While this goal is impossible with current data center designs, we thought this might be a good way to encourage “out of the box” innovation, so last year we came up with the idea was to create a temporary “data center” that used uncontrolled outside air for cooling and would be filled with servers that were cheap enough so that we didn’t care if they failed, as long as these failures were manageable.
So Christian was planning a data center, not only with no refrigeration, but also no forced air or building level fans! He considered a number of options but ended up locating the servers in a frame tent in the fuel yard behind the Microsoft Data Center.
[We] had some spare decommissioned servers we could put in a rack. So, like good Boy Scouts, we installed this rack under a large metal framed tent behind [the] data center in the fuel yard.
Inside the tent, we had five HP DL585s running Sandra from November 2007 to June 2008 and we had ZERO failures or 100% uptime.
Some of this success may be down to having a limited number of low density servers running over a short time that does not include summer, however it demonstrates that a low density fresh air approach can work. In his article Christian refers to server vendors “sandbagging” environmental parameters. That is taking a very conservative approach to setting temperature and humidity limits. Equipment can and will operate outside the parameters and in fact Green Grid member companies are being encouraged to open up the limits to enable fresh air cooled approaches.
While I am not suggesting that this is what the data center of the future should look like, I think this experiment illustrates the opportunities that a less conservative approach to environmental standards might generate. If we could achieve a PUE that is closer to the magic 1.0, we can substantially reduce the cost associated with running data centers. Just imagine never having to buy a chiller….
Christian now gets down to practical approaches that can be used today:
Make aggressive use of outside air through a process called air economization. We are already using outside air for cooling in our Ireland data center for most of the year, as the temperature very rarely goes about 80F (if you’ve been to Ireland, you’ll know why—it’s called the Emerald Isle because the grass is so green from so much rain). However, we still need mechanical cooling for those rare days when the mercury climbs above 80F. If servers had a wider environmental range, we could then eliminate the use of mechanical cooling completely and we could also use outside air in countries a little closer to the equator.
In his article Christian talks about the power inefficiency of UPS equipment where he makes some very valid points, an alternate familiar to readers of The Hot Aisle is DC Power.
Use offline UPS technologies. Most UPSs are online, in that they rectify alternating current (AC) to battery-level direct current (DC) and then invert the battery-level DC to 120 or 240 volts AC) Although this process provides better power smoothing, the double conversion is inefficient. Offline UPSs eliminate this double conversion, thus providing greater UPS efficiency. While there are the issues associated with putting unfiltered utility power to servers, there are mechanisms (such as larger capacitors in the power supplies) that can mitigate the effects of unsmoothed power. If we can achieve the replacement of online UPSs with online models, the power saving could be enormous.