Greening the data center, the hard way.


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

data center DC power plant engineering

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4 responses to “Greening the data center, the hard way.

  1. And, of course, the amount of copper needed to distribute 48V is only 8x what is needed for 240V AC.

    • I’ll grant you that 48V requires more copper than higher voltages, although I think 8x isn’t correct. So, invest in a permanent one time only infrastructure, keep paying for wasted power from double conversion UPS units, or buy 30,000 batteries that require ongoing maintenance and replacement and associated costs, contain some of the most toxic heavy metals that we use (lead, cadmium, lithium), and that you have to run hundreds and more extra servers to to make up for the ones that fail (and pay for the power for those too).

      Doesn’t sound like a contest to me.

      Vern, SwiftWater Telecom

  2. Yet, oddly, people that have actual skin in the game have determined there’s a contest. I wonder why that is.

    Also, I made a mistake — you’ll actually need 25 times as much copper (I^2 R and all that.).

    So, for a mere 25 times the cost of the power infrastructure, you can have DC, use power supplies that aren’t commodity parts, and also pay for very large UPS manufacturers.

    • Not everything that comes from Google or Facebook is the Word (enjoy your gmail account when Google blew up the routers with a dumb engineering error some time back?). I believe as a professional engineer for 25 years, I have enough skin in the game to take an opposing viewpoint when dreck is promoted as the greatest thing since sliced bread.

      1. Increasing the amount of copper in the DC portion of the power distribution system does not increase the total cost of the system by 25x. DC power plants are less expensive than double conversion UPS units and good DC power design can reduce the amount of extra copper by keeping the DC power plant as close to the load as possible.

      2. 48V DC server power supplies are FAR closer to commodity items than designing a totally new completely proprietary power supply (not to mention the entire server as well) to accommodate a 12V battery.

      3. A 48V DC power plant requires no UPS system. The DC power plant is equivalent to the double conversion UPS unit’s rectifier and battery string, minus the inverter.

      I will say it again. Any added cost in the power distribution from increased copper is more than offset by the less expensive DC power plant, good DC power design that reduces the requirement for extra copper to a minimum, eliminating the cost of 30,000 batteries, eliminating the cost of redesigning standard servers to a proprietary design to accommodate those batteries, eliminating the added maintenance costs of all those batteries, and eliminating the need to run hundreds or more extra servers to compensate for failures because you can’t possibly maintain that kind of a nightmare.

      Any way you slice and dice it, it still doesn’t add up.

      Vern, SwiftWater Telecom

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