KVM Aims for King of the Virtual Hill Status

By Paul Rubens (Send Email)
Posted Oct 15, 2009

Red Hat's KVM virtualization technology is so advanced that it will inevitably consign the Xen hypervisor to the technological scrap heap.

If Red Hat is to be believed, its KVM virtualization technology is so advanced it will consign the Xen hypervisor to the technological scrap heap, altering the virtualization landscape completely.

That's the view of Navin Thadani, a senior director of the Linux vendor's virtualization business. "We see consolidation as being inevitable, and in the medium term in this market we believe that will leave VMware, Microsoft and Red Hat," he said.

Red Hat got its hands on KVM — which works in conjunction with Intel and AMD chips with hardware virtualization support — when it acquired Qumranet, an Israel-based company, in September 2008. While the company continues to support Xen for its existing Red Hat Enterprise Linux (RHEL) 5 customers, it is being positioned very much as a legacy virtualization solution. "We believe KVM represents the next generation of virtualization," said Thadani. "KVM offers significant benefits over Xen and proprietary systems and is the strategic direction we want to go, so we will encourage our customers to start to migrate to KVM when they are ready to, and provide the tools and services needed to help them do so."

So what's so great about KVM that has caused Red Hat to prepare to abandon Xen? Most of the attraction stems from the fact that KVM is part of the Linux kernel, rather than being a separate kernel, as is the case with Xen. That means all the benefits of the thousands of hours of work done on the Linux kernel — including scalability, robustness, security, memory management, NUMA, and the vast hardware ecosystem supported — also accrue to the KVM hypervisor automatically, rather than needing to be done again. As a result, KVM can immediately support up to 96 cores and a terabyte of RAM at the host level. (Individual guest OSes can have up to 16 virtual CPUs.)

As an example of a benefit of using KVM, Thadani mentioned memory page sharing. "Memory is usually the binding constraint when it comes to virtualization. We already have memory page sharing in KVM, while this is much harder in Xen, so we can run more virtual machines on any given server with KVM," he says.

Thadani suggests another example: using KVM, every running virtual machine is a separate Linux process on the host machine. This means "bare metal" Linux apps and virtual machines can easily run side by side on the same physical host. This could be very useful in a data center that, during business hours, must run business applications that can't be virtualized, he explained. After hours, these same physical machines could be put to work playing host to a larger number of virtual machines.

Red Hat plans to provide KVM in two ways: By offering KVM with Red Hat Enterprise Linux (RHEL) 5.4, which was released in early September, or as a separate thin Red Hat Enterprise Virtualization (RHEV) hypervisor. This is effectively a KVM hypervisor that runs on bare metal, like VMware ESX Server or Xen, rather than a full RHEL installation that offers virtualization.

Which is the most appropriate offering? The full RHEL 5.4 with KVM is targeted at enterprises familiar with Linux, and those that perhaps already have their own hardened RHEL build, with customized boot scripts, and so on.

RHEV is aimed at comparative Linux newbie organizations that simply want to boot a system and start running virtual machines on it.

This sounds simple, but Thadani then goes on to complicate matters. "If you want to run primarily Linux guests, then it will make sense to use RHEL with KVM. But if you are planning a mixed environment of Windows and Linux guests, then it will make sense to buy the RHEV hypervisor as it will be cheaper to get the 'thin' product. The reasoning behind this is not obvious, but Thadani promises it will become clearer when pricing information is announced.

One of the strengths that makes VMware a formidable competitor in the virtualization space is its comprehensive management infrastructure. While Thadani promises a highly sophisticated one as well — in the shape of its Red Hat Enterprise Virtualization Manager for Servers suite — it's doubtful it will be as mature and well-rounded as VMware's offering. But Thadani is banking on the fact that in the longer term this will not matter because virtualization is becoming a central part of IT infrastructure in the data center. That means data center management systems supplied by systems vendors will have to incorporate virtual environments (including heterogeneous ones) as well as physical ones, he said. In other words, it will not be the responsibility of virtualization vendors to supply management software for their products because management systems like Microsoft's System Center or HP's OpenView (or whatever it is now branded) will have to be able to handle virtualization anyway.

There's one more part of Red Hat's KVM jigsaw puzzle that hasn't yet been mentioned, and that's Red Hat Enterprise Virtualization Manager for Desktops. It's a system that enables VDI, using KVM to virtualize Linux and Windows desktops, along with a connection broker, SPICE rendering technology and other smarts that came with the Qumranet acquisition. It's a handy technology to have, but it remains to be seen whether VDI ever takes off to the degree many vendors hope.

As for KVM consigning Xen to the scrap heap, that too remains to be seen. Although RHEL 5.4 is available now, the full portfolio of Red Hat's KVM offerings is still under development and will not be available — along with pricing details — for several months at the earliest.

Paul Rubens is a journalist based in Marlow on Thames, England. He has been programming, tinkering and generally sitting in front of computer screens since his first encounter with a DEC PDP-11 in 1979.

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