FSOSS/07
XEN : Virtualization Changes Everything
Ross Chevalier, CTO, Novell, Canada
XEN is all about virtualization. It’s a system that’s designed to help in the virtualization process of multiple types of operating systems, on multiple types of operating systems. Ross Chevalier’s talk at FSOSS/07 about the XEN project was all about assessing the current state of the project, and also giving a brief overview of what virtualization is, and how to use it.
Virtualization is taking one operating system, and making it run within another operating system. The advantage to this is that you can have one powerful system, and split it up into many virtual instances that each manage a particular task, or set of tasks. On average, only 10% of a servers resources are being utilized, so virtualization allows a user to take greater advantage of the other 90%.
The XEN project is a system designed to allow a system to be host to many virtualized systems, and also allow you to manage the resources allocated to each instance. This effectively allows you to provide more resources to where they are needed most, on demand, in real time.
Virtualization can be split up into two types, full, and para.
A fully virtualized operating system is one that has not been modified specifically to run in a virtual environment, so it is unaware that it is being virtualized. As a result, the hypervisor traps and emulates. As one of the major contributors to the Xen open source project, Novell has integrated the Xen hypervisor as a core function of its SUSE Linux Enterprise 10 platform, making Novell the first major commercial vendor to bring an enterprise-ready Linux virtualization solution to market.
Within the graphic-based YaST tool, you can create, start, stop and manage the guest virtual machines running on your host SUSE Linux Enterprise Server. every I/O and hardware instruction that is deemed privileged by the hypervisor. Typically, the overhead occurring from these trapping and emulation operations would have a significant impact on performance. However, the AMD processors with AMD-V have been designed specifically for virtualization. The Xen hypervisor interacts with the virtualization extensions in the AMD processors not only to improve performance and efficiency, but also to provide hardware based isolation between these unmodified guest operating systems running on a virtualization server. Even with these enhancements, fully virtualized guest operating systems will typically not be able to achieve the same levels of performance as paravirtualized guest operating systems. However, since it is unlikely that all operating systems of the past—or even the future—will be modified for virtualization, the main benefit of full virtualization comes from its ability to host legacy operating systems that have not been paravirtualized. The ability to host these legacy operating systems in a virtualized environment is critical to a data center’s server-consolidation efforts. This feature is mandatory for virtualizing proprietary operating systems, including those from Microsoft.
With paravirtualization, the operating system running inside of a virtual machine (known as a guest operating system) is modified to run on top of a hypervisor. A para- (or partially) virtualized operating system instance is aware that it is running in a virtualized state and has been fine-tuned for optimal performance in that environment. Paravirtualization allows the hypervisor to avoid hard-to-virtualize processor instructions by replacing them with procedure calls that provide that functionality. A paravirtualized operating system loads and runs virtual drivers that are capable of interacting with Xen to access resources on the host virtual server. In other words, it does not require complete emulation of computer devices.
For example, a virtual machine with a paravirtualized operating system wouldn’t require an emulated graphics card, eliminating the need for the hypervisor to emulate its video data. Consequently, a paravirtualized operating system requires less overhead management, resulting in improved performance.
I found that the talk was really more about exposing people to virtualization in general, and the benefits that could be had by using virtualization technology in your systems. Throughout the talk, XEN was the virtualization tool used, but I though that it was less about exposing people to XEN, then it was exposing people to virtualization.
The whole goal is to utilize your resources more efficiently. This does not only include your servers, but also your wallet. The XEN project helps users and companies to better allocate their resources, allowing them to dynamically allocate server resources to many server instances, and save money along the way by not having to purchase additional hardware that is going to be under-utilized.
XEN helps fulfill these goals by providing a robust feature set that will allow it to provide high quality functionality to servers across the globe, and all for free. Novell has helped to make the XEN project more reliable and efficient and enterprise ready, so that it can begin to start really breaking into the enterprise-computing world as a viable alternative to buying more hardware.
Mr. Chevalier’s talk wasn’t really focused so much on open source specifically, but more about what an open source product can do for enterprise companies. I think that Novell is doing something good by helping to enhance the XEN project, because it allows users to better allocate and redistribute their resources. Their main goal here is to try to get a larger market share of the enterprise world, by bundling XEN with OpenSUSE, and providing paid support.