VMware CTO Sees Linux Advantage In Virtualizing The Data Center

Two LinuxWorld speakers in San Francisco have made back-to-back predictions that Linux will play an increasingly commanding role in the rapid-growth field of server virtualization, but it's not immediately clear why that should be so.

On Thursday, VMware's CTO Mendel Rosenblum told attendees that Linux is an ideal operating system for running virtual machines in the data center of the future. That's because Linux, with its modules surrounding a kernel of key functions, is easily stripped down and specialized for particular applications.

"Linux is a highly customizable operating system. This is a place where Linux will dominate, will shine," he predicted.

A day earlier, Ron Hovsepian, CEO of Novell, the distributor of SUSE Linux, said that Linux "will capture 36% of the virtualization market by 2011," citing market research firm IDC as the source of his figures. Linux is typically adopted for its open source code characteristics -- freely available, maintained by a large community, and reliable server functionality. But Rosenblum ignored those qualities and lauded it for its modular design, the ease of adding and subtracting what's known as its tagged software "packages." The ease of add/remove in its makeup gives Linux its overall adaptability.

Rosenblum said modern operating systems try to be general purpose managers for all conceivable applications that might run on top of them. As a result, they are large and complex -- a change in one part affects many other parts.

"Even with a huge team of engineers, Microsoft had trouble doing anything" with its Vista release of Windows, dropping several wanted features because of Windows' size and complexity, he said. Microsoft and VMware compete on virtualization products. An IDC spokesman said the same report that gives Linux a 36% share of virtualization software revenue by 2011 says Microsoft will capture 52% of virtualization software revenue in the same time frame.

Nevertheless, the Linux share reflects an estimated broad use of Linux for virtualization purposes, explained IDC spokesman Michael Shire.

Microsoft charges for each copy of Windows that is used in a virtual machine, along with annual maintenance fees. Linux suppliers, such as Red Hat and Novell, usually sell the operating system on a subscription basis with no up-front license fee. They charge instead for annual support. The virtualization revenue IDC projects for Linux means that Linux will be running in a large number of virtual machines, and technical support from Red Hat, Novell, and other vendors will amount to 36% of total projected virtualization revenue.

The reason Linux will gain a substantial share of future virtualization revenue is the alignment of its design with the way virtual machines work, Rosenblum said. Each virtual machine contains a copy of an operating system and an application, along with virtualization software that allots a share of hardware resources to the VM. If the operating system has been optimized for the application, the virtual machine will perform more efficiently.

Linux's design lends itself to such optimization, said Rosenblum. The Linux kernel is limited to core functions, such as memory management. The modules that surround the kernel may manage data access or particular hardware devices. They can be added or stripped away at will without interfering with the kernel's operation.

Instead of one-operating-system-fits-all, application vendors in the future will package their software with a copy of Linux that's been optimized to run their application, Rosenblum predicted. A few do so today, producing what's known as virtual appliances. The appliance can be presented as a single file in a format ready to run in a virtual machine.

"The operating system will become more like a library," in which the customer visits and selects the parts that he wishes to use. "We like to talk about just enough operating system -- JEOS," or "juice," as Rosenblum pronounced it. "Linux is really good for these things, a highly customizable OS. ... Linux is positioned to be the operating system of choice," he added. Windows will also be a frequently used in virtual machines because of the large number of applications written to run under Windows. But Windows offers limited opportunities to be reconfigured for individual applications, he claimed.

Computer development created a choke point when it settled on the operating system as the communicator between applications and underlying hardware, continued Rosenblum, who is a professor of computer science at Stanford University specializing in operating systems. The decision has lead to an innovation choke point when one company gains a monopoly in operating systems, at least for certain classes of computers, such as IBM's mainframe systems or Microsoft Windows for x86 instruction set hardware.

That choke point will be opened up, depending on the outcome of a battle that is already under way between VMware, Microsoft, and open source Xen to supply the hypervisor on future computers. A hypervisor is an advanced form of virtualization, a thin virtualization engine that talks directly to the hardware in place of the operating system and serves that function for multiple virtual machines.

If VMware's ESX hypervisor becomes broadly established, it will sit between Windows and the hardware, managing the communications itself. It will also allow any x86 instruction set operating system above itself, not just Windows.

Xen is also a hypervisor and Microsoft is working closely with Xen to bring out its own hypervisor, Veridian, sometime after the launch of Windows Longhorn Server. Xen also talks directly to the hardware and allows a variety of operating systems above it. Microsoft has promised multiple operating system support in Veridian but, so far, as candidates to run under a Windows host.

But the prospect of being "pushed up" and away from direct contact with the hardware is something that nobody already in that position, including Microsoft, wants, Rosenblum conceded. So there "will be a big battle to see who gets to control that layer, who controls the hypervisor."