Xen 3.3.0 hypervisor ready for download
The new version 3.3.0 of the free virtualisation solution Xen has a number of revamped features and is now available to download. The new version is also available as part of a package with a 2.6.18 kernel version of Linux as the host system, also known as Domain 0 (Dom0). Xen calls guest systems user domains (DomU). According to Xen developers, the number of supported guest operating systems has grown and there are improvements in performance, the ACPI power management modes, and security functions such as using PVGrub instead of PYGrub. Xen 3.3.0 also has fewer limitations on moving running virtual machines from one physical system to another. This function, necessary for redundant fail over configurations and practical for server maintenance, has previously only been usable when the processors (and chipsets) running on the physical machines involved supported very similar hardware virtualisation functions.
The Xen documentation is somewhat vague, the Xen 3.3.0 download site links to the readme for Xen 3.2.0. A draft of the datasheet (PDF file) for Xen 3.3.0 goes into a bit more detail. This documentation contains a note that it is possible for graphics cards from the DomU to be accessed by native drivers (similar to PCI pass-through), as long the processor and chipset support Intel's Virtualisation Technology for Directed I/O (VT-d). This is the case in the newest server chipsets, such as the 5400 (Seaburg), but also in some VPro Q-series chipsets for commercial office computers (Q35 with ICH9DO, the upcoming Q45 with ICH10 and TPM). Until recently, Intel has apparently viewed VT-d as a function that should only be used for network cards; in practice, VT-d, to the extent that it was activated at all by the mainboard's BIOS, is typically limited to the onboard network chip or PCIe x4 connections and does not work in the PCIe x16 slots that PCI Express Graphics (PEG) graphics cards usually use. Until now, Xen users who wanted to run a fast 3D game that needed high-performance DirectX support on a virtualised Windows system have apparently been out of luck. Xen 3.3.0 should at least permit scaling of graphic output from the graphics chip via OpenGL.
The now two year old version 2.6.18 of the Linux Kernel is something of an impediment for some applications, as it lacks support for recent hardware – that can be a real hindrance considering that the newest hardware components are needed to run VT-d.