Hype over hypervisors

Several key Linux kernel and system-tool advancements over the last several years are helping these virtualized data-centres-in-a-box and grid-style deployments to evolve.

"The introduction of hypervisor technology you might say is the single-most important virtualization advancement over the past five years," says Justin Steinman, Novell's director of product marketing for Linux and open source.

The hypervisor is a software layer that sits between the guest operating system and the physical server. "The best way to think of it is as the traffic cop," Steinman says. The software controls the different operating systems that are running on a virtualized server and manages the flow of the hardware resources, such as I/O, storage, and processor use and memory access. Open source and vendor-specific products in this area include Xen's open source virtualization technology, IBM's z/VM and VMware's ESX Server.

Virtualization via a hypervisor layer is called paravirtualization, Steinman says, as opposed to standard VMware-style virtualization, in which a guest operating system runs inside a host, without any knowledge of the host system. Novell's SUSE Linux Enterprise Server 10 has a Xen hypervisor built into the Linux distribution, and Red Hat's forthcoming update to its Enterprise Linux Server also will have this virtualization piece built in.

"You need to put software drivers [in the guest Linux systems] to make them aware that they're being virtualized," he says. This enables the virtualized Linux systems to use processor resources more efficiently. Otherwise, the systems would compete for resources, with the software functioning as if running on a weak hardware system.

In clustering and distributed computing, some of the important advances have happened inside the Linux kernel, as well as with system and management tools offered by vendors to harness and control dozens, hundreds or thousands of Linux-based processors.

"That's a challenge for high-performance computing users," Steinman says. "How do you make sure all those processors are the exact same operating system with the exact same patch, with all the different tweaks there? If one box is out of sync, it could bring the whole system down."

Tweaks in the Linux kernel over the last few years also have expanded possibilities for distributed, virtualized Linux.

"Some of the advancements inside of Linux that have helped this stuff are improvement in scalability and performance," Steinman says. Linux software can now scale to 10TB of memory across a grid or cluster, and as many as 1,024 processors. "That's an advantage where the open source technology has improved to enable that. You could go out this afternoon and download the code and find the exact code tweak that was made to implement that kind of advancement."

Linux virtualization also is being used to consolidate Windows servers in some IT shops. Success Apparel, a children's clothing company in New York, recently boiled down its 17 separate Windows servers to nine servers running SUSE Enterprise Linux, VMware and virtual Windows instances on top.

The move "has reduced operating expenses by 25% while allowing our IT staff to concentrate on other projects," says Steven Golub, the company's IT manager.