In the virtual cloud data center, greenwashing with PUE.

This afternoon I’ve been reading about Elastra making it’s data center cloud more efficient. I’m rather skeptical that metrics meant to be applied to physical servers and facilities have any meaning on virtual ones.

The basic premise of the idea isn’t a bad one. The green benefits of the cloud come from not only more efficient use of the physical servers and infrastructure, but also efficient use of the cloud resources. Wasting cloud resources by overprovisioning memory for a virtual machine, for example, wastes resources in the underlying physical server, which, in turn, wastes data center infrastructure, costing the operator more money. Knowing exactly what an application or combination of applications really needs is a must, otherwise you might just as well stick with a data center full of energy hogging under utilized dedicated physical servers.

The problem I have with the Elastra approach is the metrics presented as a criteria for choosing the virtual configuration, such as PUE. PUE (power usage effectiveness) is simply the total amount of power a data center consumes vs the amount actually used to operate IT equipment. I have issues in general with what PUE is measuring and how the metric is being used, as I’ve written before, but I really have a problem with it in this context.

The problem is, PUE is a data center wide metric. I don’t think it’s possible to single one server out of a data center for any kind of an accurate PUE number (unless you just have one server in the data center). On top of that, how do you even come up with a PUE or even a wattage for a virtual machine that has no physical existence? Add to this the fact that PUE isn’t a static number but constantly changes as environmental conditions and server workloads change.

As I’ve said, I’m far from being against accurately provisioning cloud services for the workload to be run on them, I’m against the misapplication of green metrics intended for physical facilities to virtual machines that can’t possibly produce a meaningful number. Of course, PUE looks good on the press release, but in my book, that’s greenwash.


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3 responses to “In the virtual cloud data center, greenwashing with PUE.

  1. Vern,

    Thank you for your comments. Elastra’s platform is built to be flexible enough so you can optimize for whatever metric you have access to and use to measure energy efficiency. We expose the existing capabilities of the datacenter through our modeling languages and allow users to optimize on the available information. When information and capabilities in the datacenter change our system takes this into account.

    PUE was cited as an example of a metric that companies are using to measure energy efficiency that we could optimize for but we don’t restrict or encourage our customers to use it exclusively. We allow you to optimize for a goal but we let you define what that goal is based on the capabilities of your datacenter. As new metrics and standards in the industry emerge our system can be easily extended to allow you to optimize for them.
    I do, however, feel that it’s possible to measure the energy impact of virtual machines. Think of a scenario of having multiple VMs running on a large # of hypervisors. Is it more or less efficient to optimize the VMs so they are distributed on the lowest # of hypervisors? It’s this kind of relationship we allow customers to model in our product, which is why we feel it is a powerful platform for optimizing energy efficiency in the datacenter.

    Peter C @Elastra
    Product Manager

    • None of that do I dispute. My point is that, since every PR article I’ve seen on you lists PUE as a metric for this, I have to assume you’re the source of this usage.

      Given this, my question is still valid. If someone wants to show me how to pick the PUE of a single server out of an entire data center, much less calculate PUE for a single virtual machine, I’ll retract the designation of this story as greenwash, otherwise, I stick by it.


  2. Vern and Peter,

    PUE is a good coarse macro metric of the facility, however as mentioned already, it does not provide an indicator of effective work or productivity.

    Thats where PUE should be used in conjunction with other metrics that provide an indicator of productivity, effectiveness of how resources (server, storage, networks, software, physical data center) are used to deliver a given level of service.

    Here are a couple of blog posts that I did last fall that are related to the topic and discussion.

    Saving Money with Green IT: Time To Invest In Information Factories

    PUE, Are you Managing Power, Energy or Productivity?

    Cheers gs

    Greg Schulz, Sr. Consulting Analyst – Server and StorageIO
    Author “The Green and Virtual Data Center” (CRC) and “Resilient Storage Networks” (Elsevier)

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