Energy capping system holds promise of greener datacentres

Microsoft researchers have unveiled a tool they believe could help minimise the amount of power used by datacentres without impacting on business performance.

Typically, datacentre bosses can lower the power use – and therefore operating costs – by under-provisioning key parts of the power infrastructure, but this can lead to performance issues.

So, a team of researchers set out to find ways to make datacentres greener, without impacting business.

The team was led by Aman Kansal of Microsoft Research, along with his fellow Microsoft workers, Sriram Govindan and Sriram Sankar,  presented their findings at this week's International Green Computing Conference in San Jose, California.

Kansal and his team said they knew significant power reductions were possible if datacentre infrastructure such as uninterrupted power supplies, diesel generators or cooling systems were optimised for actual peak power loads rather than a peak power load based on sever nameplate power ratings.

Most modern servers come with power management tools that make this type of power capping feasible. Typically, these tools rely on dynamic voltage and frequency scaling (DVFS) to change the frequency at which the processor operates, effectively swapping a bit of performance for reduced power consumption.

The team tested out a variety of power capping systems, using a mock-up system based on hosting 14GB of Wikipedia copy using a handful of web servers.

However, these tests demonstrated that current DVFS tools are best suited to individual servers, rather than managing the entire server estate, especially for virtualised datacentres.

“It is more efficient to provision for the peak of the sum of server power consumptions, or equivalently, the estimated peak power usage of the entire datacentre,” the researchers said.

Furthermore, the performance changes introduced in to the datacentre by DVFS tools could not respond quickly enough to potential spikes in demand and in some cases could introduce critical instability in to the system.

So they set about developing an admissions control tool, to limit the number of requests made on servers.

“This implicitly reduces the power consumption since the processor has more idle cycles that it can spend in lower power sleep states,” the researchers said.

Tests on the Wikipedia simulation showed that when used in conjunction with existing DVFS tools, this admission control system was able to cap power thresholds at pre-determined levels, enabling the team to make acceptable trade-offs between performance and power usage.

The tool needs further fine tuning before being commercialised, but it opens up the possibility of greener datacentres in the near future.