The framework, called Kernel-based Virtual Machine, or KVM, is a full virtualization technology for Linux on x86 hardware. It consists of a loadable kernel module named kvm.ko and a userspace component. Both components are open source software.
On the Linux Kernel Mailing List archive, Torvalds announced the release with a succinct message that mentioned the usual bug fixes and patches in passing, but he focused on KVM by name: "A lot of stuff. All over. And KVM," he said.
KVM is a relatively new virtualization technology that allows a user to run virtual machines using unmodified disk images containing operating systems. Each virtual machine has private virtualized hardware with a network card, disk, graphics adapter, etc. KVM was created and is maintained by Qumranet Inc., a technology startup based in Santa Clara, Calif.
There are several similarities between the virtualization models employed by KVM and proprietary offerings like VMware Server and Microsoft Virtual Server. All three technologies run a host virtualization model. In the case of KVM, it loads onto an existing Linux distribution and can then run unmodified versions of Linux and Windows as operating system guests.
Early reviews spoke highly of KVM's ease of use and stability, but a recent benchmarking test by Phoronix, a review and benchmarking site for Linux, found it lagged behind fellow open source virtualization technology Xen 3.0.3. Xen is an open source virtual machine monitor for x86-compatible computers. KVM took the top spot in only one of five benchmarking tests.
The tests did reaffirm that the benefits of KVM are high performance and stability, however. But, even so, Gordon Haff, an analyst with Nashua, N.H.-based Illuminata Inc., reiterated previous comments made to SearchServerVirtualization.com that KVM has a hard road ahead – if one at all.
"It's not so much that VMware has been aggressive in server virtualization -- though that's certainly true. But Xen in its various forms as part of Linux distributions and as part of commercial offerings from Virtual Iron, XenSource and others has really become the standard for Linux," Haff said.
With these vendors already established and jockeying for position in the Linux virtualization space, Haff said it would be difficult for him to see what advantage having another variant brings to the table or why people would be interested. Options are always good, he said, but only to a point before they begin to cause confusion and lack critical mass.
"In fact, I'd go further and say it was the rallying around Xen of many companies that made for a viable open source hypervisor," he said.