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HPC virtualisation


A


solution


Virtualisation in HPC may not always be the answer, as Gillian Law discovers


V


irtualisation has been one of the major technology trends of the past 10 years or so. Whether it’s being used as part of cloud computing, offering


access to compute power on demand, or as a way of making better use of a computer estate within a company, it’s seen as a way to save money, save power, and save wasting vital computer resources by using all the capacity available. Yet visit any HPC centre and you’ll find a world that remains resolutely physical.


www.scientific-computing.com Virtualisation works because it makes


use of the spare capacity on underused machines. In the HPC world, there are very few of those – machines are used to their absolute maximum capacity, as far as possible, to get the most use out of them. There’s no need to leave room for spikes in demand in a situation where you know exactly what you’re going to be doing and what it will take. And then there are the performance costs – virtualisation adds considerable overheads.


‘A virtual machine is a stack of software


that includes an operating system. It moves data around to interpret it in the hypervisor, it uses storage and CPU space – so it’s always running slightly slower than a native mode application would. You’re talking about six to eight per cent, so it’s not a lot, but in a deterministic system that might matter a lot,’ says Ian Osborne, head of the ICT Knowledge Transfer Network’s enterprise IT group. Mark Parsons, executive director of


supercomputing centre EPCC in Edinburgh, agrees. The performance penalties in using virtualisation usually count against it to a degree that makes it unusable.


OCTOBER/NOVEMBER 2011 21


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