The It media reported that Sun has some issues to deliver its Xen-based hypervisor, xVM Server, in time. The release of xVM Server and the enterprise management console Ops Center 2.0 was scheduled for September 10, 2008. On that day however Sun said it wasn't able to release the virtualization solution in time and re-announced the launch.

After missing another deadline - for the release of the virtualization offering - November 2008 Sun, last week surprisingly without any press release released Ops Center 2.0, despite that xVM Server is still not ready.

The IT press published a new projection that Sun's Xen-based the hypervisor is rescheduled for Q2 2009. The French technological magazine LeMagIT unveiled that the first edition of xVM Server will not support SAN and iSCSI storage facilities.

Xen is an unique technology, a powerful Open Source industry standard for virtualization that it a set for virtualization of x86, x86_64, IA-32, IA64, PowerPC, and other CPU architectures.

The Xen's main advantage is that it allows a several guest OS to be executed on the same physical server. It makes possible each of these OS to operate in conjunction with others on the server.

Xen system is structured with the Xen hypervisor (Virtual machine monitor) as the lowest and most privileged layer. Above this layer can work guest several OS, which the hypervisor schedules across the physical CPUs. In this software infrastructure the first OS is "domain 0" (dom0). It is booted automatically when the hypervisor boots and given special management privileges and direct access to the physical server. To start any of the other OS ("domain U" (domU)), the Xen's administrator has to log into dom0.

Those who want to use have to insert Xen's software layer between the host server's hardware and the OS. This creates an abstraction layer that allows each physical server to run one or more virtual servers effectively decoupling the OS and its applications from the underlying physical server.

Xen allows modified versions of Linux, NetBSD and Solaris to be used as the dom0. Other modified Unix-like OS can installed and executed as OS operating systems (domU). In Xen 3.0, unmodified versions of Windows can also be used as guest OS if the CPU supports x86 virtualization.

Why Xen?

Hypervisors like Xen are used by web hosting companies to provide Virtual Dedicated Servers. In general, the server virtualization allows web hosts to consolidate resources, to increase utilization, and ability to respond dynamically to any faults by re-booting virtual server or even to move it to a different hardware. In virtual environment it is also possible to securely separate virtual OS, and to support legacy software as well as new OS instances on the same server.

Xen supports live migration of a virtual server from one physical machine to another. It also allows workload balancing and avoids downtime.

Xen can be used on a PC or server that run Linux and at the same time have Windows installed. Although such systems are used in a dual boot setup, Xen makes possible to start Windows "in a window" from within Linux, and to run applications from both systems at the same time.

According to Xen's website "Xen’s paravirtualization technology is the fastest and most secure virtualization software in the industry. The producers of Xen also say that it offers "near-native performance for virtual servers with up to 10 times less overhead than proprietary offerings, and benchmarked overhead of well under 5% in most cases compared to 35% or higher overhead rates for other virtualization technologies".