Tonight I was reading about Facebook following Google’s lead in putting batteries in servers in the data center. This just goes to show you’re never to big to have or share a boneheaded idea.
The idea is simple. Remove the data center UPS and add a backup battery to every server. This is far from a green solution, not to mention a serious maintenance nightmare.
The conventional double conversion UPS is one of the biggest energy wasters in the data center. In a double conversion UPS, incoming AC is rectified to DC for the batteries, inverted back to AC for the servers, and converted back to DC internally. Each conversion adds loss to the system and generates extra waste heat that requires energy to dispose of, so eliminating the double conversion UPS can make a major difference in data center power efficiency.
Now we come to the hard way to do it, putting a battery in every server. Now, consider for Facebook, that means in excess of *30,000* batteries. Consider the cost of all those batteries, the amount of toxic heavy metals involved in the manufacture of those batteries, and the near impossibility of maintaining them. Add to that the cost of proprietary retrofits to servers or complete replacement with proprietary servers and this is starting to sound like something out of a horror movie.
So, how does this even actually work for Facebook? It’s simple. Facebook and Google both have such massive amounts of redundant servers that there isn’t much impact if a few hundred to a thousand of them are broken at the same time. Just don’t think about what having a thousand extra servers running does to energy efficiency (this is why PUE is such a crock).
So, how do we eliminate the energy sucking power hog that is the double conversion UPS and not create a nightmare in the process? Simple, DC power distribution. In the data center DC power plant and DC power distribution setup, AC power is rectified to DC and the DC power is supplied directly to the servers. One conversion instead of three is a definite power saver. In this kind of plant, the batteries are simply strings that concentrated with the DC power plant and connected across the DC power distribution.
In the data center DC power plant, you have a minimum number of batteries all concentrated in one location, making maintenance a snap. Also, batteries used in DC power plants are typically designed to last far longer than anything sized to use in an individual server, drastically reducing the expense of replacing all those batteries, not to mention the ecological nightmare of all those little packages of toxic heavy metals. The added benefit is that the heat generated by the servers themselves is also reduced.
Next on the plus side is that servers and power supplies based on the standard 48VDC power, while not as common as AC powered servers, are certainly easily available, eliminating the expense of proprietary hardware design.
Finally, you’re not going to have ANY servers fail from dead backup batteries when push comes to shove. This means no more running hundreds to thousands of extra servers required to compensate for those dead battery failures.
Talk about trying to do it the hard way.
Vern, SwiftWater Telecom