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Virtualization and HPC - Will they ever marry?

Imaginary-server overhead

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SC08 Server virtualization has spent the past several decades moving out from the mainframe to Unix boxes and then out into the wild racks of x64 servers running Windows, Linux, and a smattering of other operating systems in the corporate data center. The one place where virtualization hasn't taken off is in high performance computing (HPC) clusters.

And for good reason. But as hardware costs continue to plummet, making hundreds of teraflops of raw computing power in a parallel x64 server cluster available to even medium-sized businesses, startups, academic institutions, research facilities, and other places where HPC clusters end up - and at a relatively modest price - the system administration demands on HPC labs and the desire for more flexibility may possibly - and I mean possibly - see the adoption of server virtualization technologies in this subsegment of the server space.

Roughly speaking, HPC clusters account for about a fifth of the shipments of x64 server boxes each quarter. And according to IDC, in 2007, HPC boxes of all types - including vector, cluster, and other types of gear - accounted for $10.1bn in sales (revised downward from an initial $11.6bn estimate that came out in March of this year). That gives HPC an 18.6 per cent take of the $54.4bn in server sales in 2007, again about a fifth of the piece.

But the interesting bit is that if you take HPC machines out of the picture, general-purpose sales would be nearly flat for 2007. And equally importantly, if you remove the HPC boxes from the mix, then the adoption rate on new server sales for virtualization would be a little bit higher than the broader market stats cited by Gartner and IDC.

HPC customers, as a rule, do not use server virtualization because of the overhead this software imposes. The benchmark tests that server virtualization vendors such as VMware are beginning to use - I am thinking here of VMark, but also the two-year-old SPEC virtualization benchmark effort that has yet to bear fruit - do not show the overhead their hypervisors impose.

But as the x64 platform got virtualization hypervisors a number of years ago, the performance penalty was as high as 50 per cent on some workloads, and even after hardware features to support virtualization have been added to x64 chips from Intel and Advanced Micro Devices, the overhead is widely believed to be in the range of 10, 15, or 20 per cent. But seeing as though there are no independently available tests, customers really have to do their own benchmarks. And by the way, the terms of the ESX Server licensing agreement from VMware apparently do not allow people to publish the results of benchmark tests.

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