Open source Xen hypervisor in the Linux kernel: Does it matter?

The open source Xen hypervisor has fought hard, but KVM is the new top dog in open source virtualization.

Now that the Linux kernel has full support for the open source Xen hypervisor, how will the open source virtualization

landscape change?

Five years ago, open source Xen was the next big thing in virtualization. It was free, it was open and the industry expected it to take significant market share away from VMware. That never happened, partly because the Xen hypervisor wasn’t part of the Linux kernel. That roadblock is gone, but open source Xen still faces an uphill climb, thanks to the emergence of KVM.

Where the Xen hypervisor has been
The open source virtualization market has changed quite a bit in the last few years. Because the Linux kernel didn’t fully support open source Xen, the Xen hypervisor needed a specific Linux kernel version. As a result, changes and improvements to mainstream Linux didn’t transfer to open source Xen as well. That made it difficult to keep the Xen hypervisor up to date.

Because of these drawbacks, the Linux Kernel-based Virtual Machine (KVM) hypervisor -- which is part of the Linux kernel -- became quite popular in the open source virtualization market. It wasn’t initially as advanced as the Xen hypervisor, but now KVM has more features and is easier to maintain and update.

Ubuntu included KVM as the default hypervisor for its Linux distribution in 2008, and more recently, Red Hat dropped the open source Xen hypervisor in favor of KVM with its latest release of Red Hat Enterprise Linux (RHEL). KVM is also the default hypervisor in the latest release of OpenSUSE and SUSE Linux Enterprise Server 11 Service Pack 1 (which is still in the technology preview stage). In fact, the only enterprise Linux distribution that still seems to be serious about open source Xen is Oracle’s, which offers the Xen-based Oracle VM hypervisor.

Where the Xen hypervisor is going
Looking at these open source virtualization players, Red Hat is the only distributor actively developing a solid virtualization offering. In addition to the KVM stack in RHEL 6, the company offers Red Hat Enterprise Virtualization (RHEV), a virtualization hypervisor and management platform.

The Ubuntu and SUSE distributions are important from a corporate perspective but don’t seem to have a complete vision for their open source virtualization offerings. And the fact that Oracle still focuses on open source Xen doesn’t mean much, because Oracle is a small player in enterprise Linux.

The Linux kernel added support for the open source Xen hypervisor earlier this year, but the move isn’t likely to bring significant changes to the market. The open source virtualization world has chosen KVM, and with the biggest player in that world -- Red Hat -- focusing on KVM, including Xen in the Linux kernel isn’t going to give the Xen hypervisor much of a boost.

This was first published in August 2011

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