Virtualization is a hot data center technology that is capturing the attention of IT for its consolidation and cost saving potential. As was evidenced at the LinuxWorld conference in San Francisco last week, open source and Linux platforms are on the forefront of the trend. In fact, given licensing issues with proprietary software, the combination of inexpensive or free open-source software and virtualization platforms may be the most important vehicle to drive widespread Linux adoption in the data center. Here are seven need-to-know points when looking at open source virtualization technology.

The Zen on Xen

Xen hypervisor is an open source virtualization engine developed by the founders of XenSource, which produces commercial virtualization software built off the Xen platform. Xen is delivered as an "engine" and developers can build components around it for their particular deployments, be they servers, clients, PDAs or embedded.

RONS (Red Hat, Oracle, Novell, Sun)

All these vendors offer virtualization technology based on the Xen hypervisor. The difference is that each has modified Xen in that open-source-kind-of-way to suit their specific needs and goals.

Kernel Based Virtual Machine (KVM)

KVM is the first virtualization technology to be part of the mainline Linux kernel (V2.6.20). It is designed for x86 hardware containing virtualization extensions (Intel VT or AMD-V). KVM includes a loadable kernel module and a processor-specific module, and runs both Windows and Linux virtual machines. Each virtual machine has private virtualized hardware, including a network card, disk, and graphics adapter. The first ever KVM conference is Aug. 29-31 in Tucson, Ariz.

KVM vs. Xen

KVM runs only on Linux, but on the upside it can take advantage of features such as memory management. Like Xen, KVM has the potential to scale (another inherited Linux trait). And like Xen, KVM's power management, one so-called green feature, could use some help, and its memory support is weak. Xen has better management features and, obviously, runs on more platforms In addition, it supports paravirtualization, which in general is a technology that creates a proxy between the guest operating system and hardware.

What's your type

A Type 1 hypervisor like Xen runs right on the hardware platform. A Type 2 hypervisor runs within an operating system, creating a stack that includes hardware, operating system hypervisor, and guest operating systems.

If you build it, they will virtualize

Users have to build an ecosystem around virtualization, and it has to support both Windows and Linux, says Simon Crosby, CTO of XenSource. The ecosystem requirement, he says, includes building on the virtualization platform to support storage virtualization, security and management capabilities.

Host emulation and other platforms

QEMU, Bochs and VirtualBox are examples of host emulation technologies that fall into the virtualization category and support various guest operating systems. Virtual Box has an open source edition that was released in January under a GPL. Its unique features include running virtual machines remotely over the Remote Desktop Protocol, iSCSI support and USB support with remote devices over RDP. OpenVZ is a Linux kernel modified to include the OS-level virtualization technology (adapted from SWsoft's Virtuozzo). It is licensed under GPLv2.