Everything Xen
January 18th, 2008 | 
Author: Try to see it once my way
Everything Zen
Everything Zen
I don’t think so
Xen, XenSource, XenServer, and Zen. What are they? Which one do I use to virtualize my servers? What is Citrix’s product and how does it compare to VMware? These are my reasons for writing this post. Frankly, I was confused. After some intense meditation I decided to figure it out. Unfortunately, Lakers coach Phil Jackson was not available to help.
Wikipedia was where I started my journey. At first I was even more confused when I landed on the Xen (disambiguation) page:
“Xen” is a common misspelling of Zen.
The word Xen can mean:
· Xen, an open source virtual machine monitor, developed by the
· Xen, a research programming language for type-safe XML access, now part of C?
· Xen: Ancient English Edition, a science-fiction book by D.J. Solomon
· Xen Cuts, compilation album from independent London-based record label Ninja Tune
· Xen (Half-Life), an alien border world in the science fiction computer game Half-Life
I was really tempted to go to the alien border world, but the path to enlightenment requires focus. Wikipedia’s Xen page was much more helpful.
Xen originated as a research project at the University of Cambridge, led by Ian Pratt, senior lecturer at
Xen is a Linux, host based, free virtual machine monitor that allows several guests to run and share the host’s resources. As of Xen version 3.0 unmodified versions of several Windows OSes can run in Xen. OK, Xen is like Microsoft’s Virtual PC or VMware’s Workstation/Player. Cool, I could reformat my notebook with Linux, install Xen, and get my company IT department to put our corporate XP image in a VM I created. Well, maybe that is not a good idea from a desktop support point of view.
Something unique about hosted Xen VMs also discovered on the Wikipedia page:
Xen virtual machines can be “live migrated” between physical hosts across a LAN without loss of availability. During this procedure, the memory of the virtual machine is iteratively copied to the destination without stopping its execution. Stoppage of around 60–300 ms is required to perform final synchronisation before the virtual machine begins executing at its final destination, providing an illusion of seamless migration.
This is comparable to Vmotion with VMware ESX and shared storage. However, there is no mention of shared storage being a requirement. I’ll have to try that some day with Xen.
So, does Xen come in a VMware Server and/or ESX-like flavor? Yes to both:
Xen can be delivered to market as a virtualization platform, such as Citrix XenServer Enterprise Edition (formerly XenSource’s XenEnterprise), or embedded within the host operating system. An example of the latter configuration is the inclusion of Xen in Novell‘s SUSE Linux Enterprise 10 distribution, Red Hat‘s RHEL 5/Fedora 7, Sun Microsystems‘ Solaris, or Debian‘s Etch release. XenSource recently announced that Dell will incorporate Citrix XenServer OEM Edition as an embedded hypervisor installed in flash memory as an option on all Power Edge Servers, early in 2008.
XenSource is also developing a compatibility layer for Windows Server 2008 hypervisor, so that systems that have been modified to run as Xen guests will be able to function on the 2008 hypervisor.
After reaching inner peace with the basic Xen concepts, I was ready to explore Citrix’s XenServer (formerly XenSource). I went straight to the source at Citrix’s XenServer page:
With Xen virtualization, a thin software layer (known as the Xen hypervisor) is installed directly on the hardware, or “bare metal,” and is thereby inserted between the server’s hardware and the operating system. This provides an abstraction layer that allows each physical server to run one or more “virtual servers,” effectively decoupling the operating system and its applications from the underlying physical server.
Citrix XenServer is similar to VMware ESX. It has it’s own operating system and installs directly on the bare metal.
The inventors and lead developers of Xen, with the rest of the Citrix XenServer product team, take this powerful virtualization engine and build out a full managed virtualization platform around it, designed for efficient management of Windows and Linux virtual machines. Citrix XenServer v4 combines the performance, security, and openness of the Xen technology with XenCenter comprehensive management — a platform perfect for rapid adoption of virtualization for server consolidation, software development and test, virtual desktops, and business continuity.
Citrix XenServer v4 is a native 64-bit virtualization platform, with the scalability required by business-critical applications. The highest host and guest CPU and memory limits available, coupled with fine-grained resource controls for CPU, network and disk, enable it to deliver optimal quality of service.
XenCenter is the manager of multiple XenServers like VMware’s Virtual Center Management Server
Citrix XenServer includes XenCenter, a powerful graphical virtualization management interface that runs on any Windows desktop machine – no dedicated system is required to use its powerful unified management capabilities. When used with Enterprise Edition, it offers:
· Full lifecycle management for all your virtual machines from creation, starting and stopping, to reboot, and uninstalls
· Interfaces for creating new virtual machines from original sources or from network repositories, and for cloning them from pre-configured templates for efficient buildout of virtual infrastructure
· Ability to suspend and resume virtual machines on the fly
· XenMotion management for live relocation
· Global resource pool configuration
· Integrated configuration of virtual storage repositories and networking
· Real time and trended graphing of virtual machine and total server performance metrics including CPU, memory, plus disk and network I/O
· Controls to adjust virtual machine resource allocation as demands change
Finally, Wikipedia taught me about Zen too:
Zen (Japanese: ?) or Ch’an (Chinese: ?) is a school of Mah?y?na Buddhism notable for its emphasis on mindful acceptance of the present moment, spontaneous action, and letting go of self-conscious, judgmental thinking
That’s kind of appropriate for a VMware consultant learning about Xen, don’t you think?
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