Xen startup Virtual Iron breaks ranks on paravirtualization

Virtual Iron questions the wisdom of paravirtualization while promoting unmodified operating systems to members of the Xen community.

Virtual Iron Software, which expects to launch its Xen-based server virtualization platform in the coming months, is working to promote the idea of running unmodified operating systems on Xen, rather than "paravirtualized" operating systems.

"We have a contrarian stance on paravirtualization than the rest of the Xen community," said Chris Barclay, Virtual Iron director of product management. "Paravirtualization is very painful for the customer and without giving you sufficient performance gains," he said.

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The pain comes from being limited to a handful of paravirtualized operating systems that run on the Xen hypervisor, i.e., Novell's SUSE Linux Enterprise 10. Red Hat has also said it will support paravirtualization in RHEL 5. These distributions have had their kernels modified to access physical hardware resources directly, rather than through the hypervisor.

But that leaves a vast number of x86 operating systems that cannot run on Xen. "Customers are reticent to change their OS if it isn't broken," Barclay said. "And what if your OS distributor doesn't support the new [paravirtualized] version?"

"Full virtualization" as practiced by VMware Inc. and Microsoft, on the other hand, presents an emulated hardware layer that intercepts all calls to physical resources. This approach causes additional overhead but gives users full freedom in deciding which operating system they want to run.

To be fair, it is possible to run unmodified operating systems on Xen, but "in limited ways," Barclay said. For example, you cannot run a virtual server (Virtual Iron's term for virtual machine) on more than one CPU. Virtual Iron's Xen hypervisor will allow you to create virtual servers that span up to eight CPUs and support up to 96 GB of memory.

"We believe that VMware is spot-on in supporting any unmodified OS," Barclay said.

Virtual Iron 3.0, which is currently in beta, will therefore allow users to run generic, unmodified Linux operating systems on the Xen hypervisor. Going forward, it will also support Windows 2000 and 2003. "They're already running in our labs; it's just a question of [quality assurance]," Barclay said.

Other Virtual Iron 3.0 features include native support for 64-bit operating systems, virtualization services and management utilities that are analogous to VMware's ESX and Virtual Center. The list price will be about 40% of a comparable VMware Virtual Infrastructure 3 license, the company said.

To make up for the performance increases you get from paravirtualization, Virtual Iron 3.0 relies on the virtualization-enhanced chips from Intel Corp. and Advanced Micro Devices Inc. that are starting to come to market.

The promise of these virtualization-enhanced chips is huge, said Tony Iams, senior analyst with Ideas International in Rye Brook, NY. "In theory, with these [chip] extensions, you no longer need paravirtualization," he said. The reality, however, is different. "Intel-VT and AMD-v are still quite immature," Iams said, and he does not expect them to be found in production environments until 2007 at the earliest.

"There are a lot of things that need to come together for these chips to work: optimizations in the hypervisor, the firmware, the guest OS…." said Iams. "All of this just takes time."

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