For years, Xen and VMware have been the virtualization technologies of choice for open source operating systems vendors. With Red Hat's acquisition of Qumranet yesterday and its competing Kernel-based Virtual Machine (KVM) open source hypervisor the winds of change may be blowing, or not.

While Red Hat is now betting at least $107 million that KVM is the future of virtualization, other vendors in the open source virtualization space aren't so sure.

Red Hat executives claim that it's not a hypervisor war, and that they are now engaged in a battle with only one other vendor that has an end to end platform, namely Microsoft. Among those that participate in the open source virtualization market, Citrix, Sun, Novell, VMware and Oracle all have a stake and few agree with Red Hat's vision.

Simon Crosby, the CTO of Citrix's virtualization and management division in particular has some harsh views on Red Hat's virtualization market positioning. In his view, Red Hat is an OS vendor and their direct competitors are other OS vendors like Novell and Oracle on the Linux side and Microsoft on the Windows side.

"They do not compete in the market for bare-metal or general purpose virtualization systems and certainly have nothing to do with the broader application delivery space. Crosby told InternetNews.com. "Their only interest is getting some level of virtualization built into the Linux OS so that Red Hat Linux is not at an even further disadvantage to Microsoft once Hyper-V begins shipping as part of Windows Server."

Crosby argued that it is Citrix's belief that the majority of the market will want bare-metal virtualization systems like XenServer and VMware ESX with some segments wanting virtualization built into the Windows OS through Hyper-V.

Crosby did acknowledge that Red Hat has been a useful contributor in the Xen.org project and that Xen is an integral part of Red Hat Enterprise Linux (RHEL) version 5. Red Hat has already publicly stated that it will continue to support Xen as part of RHEL.

However Red Hat has argued that KVM can offer certain management and performance gains over Xen, which is also something that Crosby takes issue with.

"KVM benchmarking is extremely selective," Crosby commented. "Where it does benefit in performance, it does so by sacrificing what we view as fundamental security concerns for enterprise virtualization deployments. Xen's deep separation of trust domains costs a bit in performance but provides the hard-line separation required for any secure deployment of virtualization."

Crosby argued that in general KVM is only as secure as the Linux host OS which is where the weaknesses may lie.

"We believe that the KVM / Linux model for virtualization is insecure at a fundamental level," Crosby claimed. "And any performance gains that Red Hat claims will be due to the inclusion in the Linux kernel of eminently attackable code."

Next page: Novell supports KVM, to a point.