But Xen's hypervisor virtualization has its constraints, too. In practical terms, there are initial limits to Xen's ability to permit different operating systems to run. For example, Novell has said its Xen-based SLES 10 servers won't provide enterprise support for the use of RHEL, Microsoft Windows, Solaris or earlier versions of SLES until early 2007.
Even then, that support will be offered only when customers are running unmodified operating systems (which Xen can do with appropriate hardware support in the latest Intel and Advanced Micro Devices chips). Support for "paravirtualized" operating systems, which have been explicitly modified for virtualization so that they run faster, won't be supported until later in 2007, Novell said.
As for Red Hat, it will support RHEL 4 and RHEL 5 running paravirtualized on Xen, the company said. It isn't yet clear whether SLES will work on those RHEL servers. In addition, Red Hat will certify the stability of the Xen Foundation's products on only machines running fully virtualized operating systems, leaving it to individual operating-system providers to certify that their products actually work in that situation.
Political obstacles
Whether a customer uses Xen, VMware or
containers, the rationale for the adoption is the same: efficiency. When IBM
monitored a sample of its customers' x86 servers, it found that the machines'
processors showed an average of 6 percent utilization. The best company hit 13
percent average utilization, he said--still a very low number. "That's what
needs to get fixed," Gabriel Consulting Group analyst Olds said.
Ultimately, technology limits and efficiency incentives are only part of the picture. Virtualization means that computing resources move from the domain of departments and divisions and become the purview of centralized administrators.
"Anything that is a loss of control is a loss of budget and loss of power," Olds said. "The real hurdle to virtualization is less technical, and more cultural and political."
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