XenSource, a developer of virtualization solutions for Linux, has deepened its partnership with Microsoft. The two companies agreed to share information and develop code that will enhance the performance of Xen-enabled versions of Linux when running as guest operating systems under the upcoming hypervisor-based Windows Virtualization technology (which will be offered within six months of the ship date of Windows Longhorn Server, expected by the end of 2007). The new software will enable virtual machines (VMs) running Xen Linux to be portable between Windows Longhorn servers and servers running Xen's hypervisor-based XenEnterprise OS without incurring a performance penalty.

Providing this level of portability and performance requires both a common file format for storing virtual machines on disk and an API translation layer for Xen-enabled Linux VMs to run on Longhorn Server. Xen has already licensed Microsoft's Virtual Hard Drive (VHD) file format and will use it for Xen VMs. As part of the new partnership, XenSource has committed to writing the second piece, the API translation layer, for the Windows hypervisor. Given identical hardware, this code will allow Xen VMs to run with similar performance under either the Windows or XenEnterprise hosts.

Although Microsoft did not announce a reciprocal agreement to write an API translation layer so that Windows VMs can exploit the XenEnterprise hypervisor, the agreement should give both companies a boost in their battles with hardware virtualization rival VMware.

Microsoft and XenSource disclosed several other details: By Oct. 2006, XenEnterprise will support existing Windows guest operating systems (albeit using the slower hardware emulation mode), and Microsoft agreed to provide support to Microsoft Virtual Server customers running Xen-enabled Linux guest operating systems. (Microsoft didn't agree to support Linux in general, but rather to help those customers rectify problems with Virtual Server hosts.) Microsoft also announced plans to release a beta version of its Windows Server virtualization add-on for Longhorn by the end of 2006, and XenSource announced that a beta version of the Microsoft-XenSource virtualization technology will be available in the second half of 2007. Both companies also agreed to work with the Distributed Management Task Force (DMTF) to standardize protocols for managing virtual infrastructure.

Although development resources are being provided by both companies and XenSource has opened an office near Microsoft's headquarters in Redmond, WA, no financial details of the multiyear agreement were disclosed.

Microsoft's virtualization plans are described in "Virtual Server Free, Linux Guests Supported" on page 5 of the June 2006 Update. It is also described in "Changes to Server Virtualization Roadmap" on page 14 of the Jan. 2006 Update.

A whitepaper describing the Xen-Microsoft technology is available at www.xensource.com/files/msxs_whitepaper.pdf.