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<< Part 3 - Considerations while choosing a virtualization Platform

1. 1. Xen.
      1. Guest OS’s Supported. |outline
      2. Driver’s Support. |outline
      3. Speed of Guest OS. |outline
      4. Ease of Mangement. |outline
      5. Support.

Comparisons of Virtualization Software.

Based on the parameters in the article on considerations for choosing a virtualization platform, it’s time to move into a little more detailed explorations of the various Hypervisor based Virtualization Software. We’re going to look at three Hypervisors, namely Xen, Virtuozzo, and Microsoft’s Hyper-V.

Xen.

Xen is an Open Source Virtualization Software. It was originally developed by the University of Cambridge Computer Laboratory and is now released under the GPL license.

Since Xen is open source, it is widely used and has a large support community. Major chip makers like Intel and AMD have contributed to source code for Xen in order to enable it to utilize certain CPU architectures.

Guest OS’s Supported.

Xen requires the Guest Operating Systems to be enlightened. This means that if you want to run certain OS’s using Xen as the Virtualization platform, they have to be modified to make them aware that they are running on a hypervisor and not real hardware. This isn’t usually a problem since more and more OS’s are now offering packages that make them enlightened.

Even open source OS’s like Ubuntu now have packages that enable it to be enlightened. In fact, they have had it for quite some time now.

However, there are restrictions on which versions of Windows can run. All Windows Products after Windows Vista SP1 can be enlightened and even Windows XP SP3 can have this patch applied.

However, Intel and AMD have brought out special CPU’s namely Intel VT and AMD V respectively that allow guest OS’s to run on them unmodified. This means that if the CPU supports any of the above technologies, the guest OS’s need not be enlightened can can be run “as is”.

Driver’s Support.

Xen takes an interesting approach to the Device Driver problem. In order to run Xen, one of the guest OS’s must be special. It means that one guest OS must be Prima Inter Pares, or the First among equals. This special guest OS is called, in Xen terminology, dom0.

Xen puts all the headache of device driver management on the dom0 guest OS. This is a good thing, because most OS’s already have native support of the most common hardware, and the dom0 is no exception. For the record, the dom0 is usually Linux. The dom0 then interfaces with all the other guest OS’s and provides them with the illusion of their device drivers accessing the hardware directly.

If the guest OS’s are enlightened, then the drivers will know that they are not dealing with real hardware and will generate appropriate instructions.

Overall, the driver support for Xen is fairly robust and there are many different solutions depending on the type of guest OS and whether they are enlightened or not.

Speed of Guest OS.

Compared to other Virtualization solutions like VMWare, Xen is noticably faster and can host more Guest OS’s. The speed of a guest OS running on Xen is almost the same as that of Linux running directly on the hardware.

Ease of Management

Xen has a large number of management tools. Since it is open source, several management tools are open source as well including Xen Tools, Ganeti. There are plenty of options here and you can pick and choose.

Support.

Even though Xen is open source, you can still get paid support via Citrix Sytems which distributes an Enterprise Version of Xen for Mission Critical Business. If you don’t want to go for paid support, there is a large community base which will readily answer your questions. Of course, you may not get the specific and speedy help that you’re looking for.

This is a great advantage in using Xen. You can use it either as a test deployment, or as an outright solution. If you go for the latter, you can opt for the paid Enterprise version.

>> Part 5 Virtuozzo Overview

This entry was posted on Thursday, November 13th, 2008 at 12:47 pm and is filed under Blog Posts, Server Virtualization. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.