Staff Writer, CNET News.com
BOSTON—In just a few short months, an open-source software package called Xen has been catapulted from obscurity to the limelight as many computing industry powers throw their weight behind the project.
Xen lets multiple operating systems run on the same computer, a feature that's useful for extracting as much work as possible from a single system. The technology is common among high-end servers today, but on mainstream systems it requires proprietary "virtual machine" software from EMC subsidiary VMware.
At the LinuxWorld Conference and Expo here, numerous companies voiced Xen support in the form of endorsements, programming help and software contributions. Sun Microsystems, Hewlett-Packard, Novell, Red Hat, Intel, Advanced Micro Devices and Voltaire all are involved, but one of the more interesting allies is IBM, which has decades of experience in the area.
"Two or three months ago, it wasn't on anybody's radar. Now it's going to make a big change in how everyone uses Linux," said Chris Schlaeger, vice president of research and development for Novell's SuSE Linux.
The change illustrates what can go right in the world of open-source software: a project can trigger a cascade of cooperation by multiple interested parties. When it works well, as in the case of Linux, that cooperation can lead to a unified, fast-developing project rather than proprietary, mutually incompatible competitors.
"The open-source community has finally decided to smooth over its differences and get behind one virtualization project, which means it's actually going to happen rather than having 12 warring fiefdoms, each with about two soldiers," said Illuminata analyst Gordon Haff.
Xen began three years ago at the University of Cambridge in England, said Ian Pratt, project leader and a founder of XenSource, a start-up that develops and supports the software and is trying to make it a standard computer feature. "Being ubiquitous on Linux is the first step to that," he said.
Xen and other approaches to dividing a computer into separate partitions rely on a concept called virtualization, which lets programs run on a software simulation of actual hardware. In the case of VMware, this foundation is called a virtual machine.
One difference between VMware and Xen: The former completely simulates a machine, which theoretically allows any operating system to run unmodified on a virtual machine. Xen, on the other hand, uses "paravirtualization," which doesn't go as far. That means faster performance but also requires an operating system to be modified to run, Pratt said.
Higher-level software, however, doesn't need to be modified, he said.
The requirement for a modified operating system will loosen with Intel's coming Vanderpool Technology, or VT, due in 2005, Pratt said. It will mean unmodified operating systems will run on Xen, though not as fast as modified ones. That means Windows will run on Xen even though open-source programmers don't have access to change Windows itself.
Falling by the wayside
Xen competitors that haven't caught on include Plex86 and User-mode Linux. While the latter made it into the most recent version of SuSE Linux from Novell, it likely won't last.
"User-mode Linux is most likely dead," Schlaeger said. The management tools Novell developed to administer that software will be re-used to control Xen instead, added Markus Rex, general manager of SuSE Linux.
Xen will likely be incorporated into Novell's upcoming SuSE Linux Professional 9.3 and later into the next version of its premium product SuSE Linux Enterprise Server, Rex said.
Linux seller Red Hat also has Xen plans. The virtualization package is being added to Red Hat's experimental Fedora Core 4 product and will probably be in version 5 of Red Hat Enterprise Linux, said Paul Cormier, executive vice president of engineering. Like Novell, Red Hat plans to add management tools to control aspects such as the creation or removal of Xen virtual machines.
Hewlett-Packard strongly endorsed Xen this week, saying it will contribute software to the effort. "Our expectation is that Xen will provide a viable, open-source alternative in virtualization platforms," said Martin Fink, vice president of Linux, in a keynote address at the Linux show. HP, too, hopes to profit from software to manage virtual machines.
Intel began contributing software to the Xen project in January so it could use VT extensions, said Phil Brace, director of marketing for Intel's digital enterprise group.
Expanding into new areas
Currently Xen works with Linux on computers using x86 processors such as Intel's Pentium, but efforts are under way to extend it into other domains. This week, AMD announced it's helping to bring Xen to 64-bit x86 chips such as its Opteron, future generations of which, employing "Pacifica" technology, will have new virtualization support.
There's experimental support for Intel's Itanium family now in Xen, Pratt said. And IBM has expressed interest in moving it to the Power chip, Schlaeger said.
Among operating systems, the NetBSD variant of Unix works on Xen—and the version was done so quickly, Pratt said, that XenSource hired the NetBSD programmer who did the work, Christian Limpach.
And Sun's Solaris—which the company has begun aggressively pushing for x86 servers—is another likely candidate, said John Fowler, executive vice president of Sun's network systems group. "We think the open-source virtual hypervisor is the way to go," he said. (Hypervisor is a term IBM is trying to trademark referring to a layer of software that lets hardware be divided up so multiple operating systems can run on it.)
The IBM connection
Sources familiar with IBM's plans expect Big Blue to play a significant part in Xen. The company has decades of experience in the field with mainframes, Unix servers and Intel-based servers.
Although IBM has a sales and development partnership with VMware, it also has an in-house hypervisor project for x86 chips—a project that came to light in a January posting to the Xen mailing list. Researchers in IBM's labs were using it as a foundation for a project called sHype, or Secure Hypervisor, to make virtual machines less susceptible to attack. The software uses rules that govern administrative privileges and the flow of information between virtual machines.
"We now plan to contribute this to Xen by integrating our security architecture into it," IBM researcher Reiner Sailer said in the posting. Pratt responded favorably in his posting: "It'll be great to have IBM contributing to Xen security."
That's not all. One source familiar with IBM's plans said the company expects to contribute software for two key computing technologies—input-output services for communicating with devices such as network cards and virtual memory for extending physical memory using hard drives.
Despite the Xen support, IBM reaffirmed its VMware ties Thursday. "IBM has a strong and vital business relationship with VMware. That relationship is stronger than it's ever been," said spokesman Jim Larkin.
VMware, for its part, labels Xen a "nascent" virtualization project that's hampered by its requirement that the operating system be modified. "Xen will not be very useful for the overwhelming majority of customers that have deployed standard Linux operating systems today," VMware said in a statement.
But VMware—combined with Intel's VT technology and Microsoft's competing Virtual Server—faces a definite threat, Haff said.
VMware has higher-level VirtualCenter and VMotion management software, Haff said, but the core virtualization product is crucial to the subsidiary. "It's where most of their money comes from today," Haff said.