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.