Xen Pushes Paravirtualization

By Jason Brooks  |  Posted 2005-11-07

Xen Pushes Paravirtualization

If youve been keeping tabs on virtualization news during the past several months, theres a good chance youve heard about Xen.

Xen, an open-source software project that began its life at the University of Cambridge, aims to virtualize operating system instances and to do so better than current options such as VMware Inc.s products.

Rather than re-create a machine within which any operating system may run, Xen takes a "paravirtualization" tack—entire operating systems may run atop Xen, but their kernels must be modified to do so.

This approach means less operating system flexibility than you get from VMware; for example, Windows wont currently run on Xen. But the reduction in overhead incurred by running virtualized instances—as well as the projects free GNU GPL (General Public License)—has generated quite a bit of interest.

While Xens future seems bright, its present is somewhat murky. The next major release of Xen, Version 3.0 (the current stable release is 2.0.7), has been held up for months.

Version 3.0 will support Advanced Micro Devices Inc.s AMD64 architecture, symmetric multiprocessing, guest operating systems and a set of other features. Prerelease code is now available, but discrepancies between this prerelease code—which Red Hat Inc.s Fedora and Novell Inc.s SUSE Linux ship with—and the 2.x code—which Debian is targeting—have further clouded the Xen waters.

Next Page: Taking Xen for a spin.

Taking Xen for a


Xen can run with linux or NetBSD as its host operating system and can accommodate Linux, NetBSD and FreeBSD guests. Red Hat and Novell are among the vendors rushing publicly to embrace Xen as the core of their future virtualization efforts. Novells SUSE Linux 10.0 ships with rudimentary support for Xen out of the box and a graphical tool for creating Xen instances.

We encountered quite a few problems in our tests when we installed and ran—or tried to run—Xen on the Debian, Fedora and SUSE Linux distributions.

Although SUSE Linux 10.0s built-in Xen configuration tools look promising, they leave out some key steps in the setup process. For example, its necessary to configure a host domain to reserve memory for the guests it will accommodate, but the SUSE Linux tools dont include this step. Several times in our testing of Xen and SUSE Linux 10.0, the virtual machine creation tool simply died, leaving our proto-instance in an indeterminate state.

The simplest way to get Xen up and running is to download the LiveCD demo from the project, available at www.cl.cam.ac.uk/Research/SRG/netos/xen/downloads.html. This disk includes Xen 2.0.6 running on a Debian host with Debian, FreeBSD and NetBSD guests preinstalled. Easy startup scripts launch the machines and open virtual network computing sessions.

Next Page: Looking ahead.

Looking ahead


A company called XenSource Inc. was formed to productize the Xen technology, but it has yet to release any services or products. Well be interested to see if XenSource has a more mature Xen up its sleeve.

In addition, forthcoming hardware platform additions from Intel Corp. and AMD promise to enable the Xen approach to work with unmodified operating systems, such as Microsoft Corp.s Windows .

Click here to read more about Intels and AMDs virtualization plans.

For Xen truly to realize its potential, however, it will need solid participation from Linux distributors, the BSDs and Sun Microsystems Inc., which has trumpeted eventual support for Xen. The technology also requires much better packaging and integration not only for creating and running instances but also for managing them.

Senior Analyst Jason Brooks can be reached at jason_brooks@ziffdavis.com.

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