Google Data Center Secrets?: Considering “per server” Backup Batteries

Vernon Burke, SwiftWater Telecom 207-399-7108

Recently, Google released a number of details about their formerly closely guarded data center techniques. In this article I take a look at the “per server” battery backup model. This model involves DC power distribution with individual backup batteries in every server.

The first item to look at is power efficiency. The claim is that placing the battery in the server reduces power loss and approaches 100% efficiency. On quick examination, we see that the power has to travel the same overall distance from the supply to the server regardless of where the battery is located in the circuit. So, what “efficiency” does this increase?

Placing the battery in the server increases the runtime of the server given the same battery capacity, since the finite amount of power in the battery is not being chewed up by losses in the cable to get from the battery to the server. Considering the tiny amount of time these servers will spend running from the backup battery, any efficiency gain is minuscule to start with. Consider also that the battery must be recharged from the power plant as well. It doesn’t matter whether you add more loss to the charge side of the battery and less to the load side, the overall loss and therefor the overall efficiency remains the same.

What Google does end up doing is shifting the loss from the battery (which can least afford it) to the main supply (which can most afford it). Not a bad move but not a miracle energy efficiency step.

Now, add on the cost of tens (hundreds?) of thousands of batteries, the maintenance of those batteries, and the ecological impact of disposing of them as they fail, and this becomes a really questionable proposition.

Finally, consider that this scheme only works for Google because there are so many redundant servers that they don’t really care if a significant percentage of them fail on power changeover because the batteries are bad. This method of operation would result in catastrophe for any normal data center provider that attempted it.

In summary, unless the laws of physics have somehow been repealed, the source of the claimed efficiency increases is not apparent, nor does the technique appear to be applicable to the vast percentage of data center providers.


2 responses to “Google Data Center Secrets?: Considering “per server” Backup Batteries

  1. Hello Vernon,

    Your not seeing the entire picture. A typical setup has several large industrial UPS systems (takes up space). These are then connected to the racks by PDU systems (upwards of $2,000 each, each rack would need 4 or 5 of these units to power all the servers in the rack). That coast alone would cover batteries (which by they way only need less then 3 minutes of run time..why? Because the backup generator kicks on after 30 seconds of power loss).

    The run time of these very small batteries on each server is not equal to the same run time from an industrial setup. They only need power for a few minutes before the generator kicks on. So the actual amount of materials used is less.

    In all they save on the ‘infrastructure’costs, saving a ton on product (all those PDU (power distribution devices that will provide the power to the servers in the rack), installation, maintenance (support contracts) and space. Not to mention with all those rpdus you now have more devices on the network that have to be managed..and those have a failure rate as well.

    Spec out a system from a UPS company to power the same amount of servers google has and you will see what I mean. It’s a matter of time before Dell and IBM ship with small 2-3 minute run time batteries in their servers (which can be monitored in the operating system easily – and integrated in to network node management software to alert when replacement is needed- this is already being done).

  2. Dave:
    This is a fairly old post and I’ve become aware of the details of this since then. Check out this post for an up to date look at this and why I think it’s still a bonehead idea.


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