2. A Brief History of Xen
• Originally part of the XenoServers project in the late '90s
o worldwide network of compute resources
• Keir Fraser worked on it as his PhD project
• 2002 - Xen Open Sourced
o First hypervisor to champion the idea of paravirtualization
o Full, efficient secure virtualization on non-virtualizable
hardware
• 2005 - XenSource formed to commercialize Xen
o Proprietary management tools for Open Source core
• 2006 - Microsoft and VMware adopt paravirtualization
• 2007 - Citrix acquires XenSource
o Separate Xen.org formed to manage open source project
• 2009 - Xen Cloud Platform
• 2010 - XenClient
3. Xen.org? Open Source? Citrix?
• Core of Xen is all Free Software
• Possible to put together a completely functional system
o many people do
• That gives you a commodity baseline
o coordinated by xen.org, contributors from everywhere
• Many companies offer products derived from the free base
o Citrix
o Oracle
o Novell
o etc
• They add support and advanced features
4. Xen Compared to...
• Xen has a "thin hypervisor" model
o hypervisor has no device drivers, very little smarts
o is just there to keep "domains" isolated
o ~2MB executable
o relies on service domains to do lots of its work
• VMware ESXi is similar
o but also has device drivers
o and base of management stack
o hardware support depends on VMware writing drivers
• Hyper-V very similar to Xen
o Designers explicitly modelled it after Xen
• KVM has a very different model
o Linux kernel as hypervisor
15. So what did all that mean?
• Xen keeps the hypervisor job separate from:
o management OS
o management stack
o device drivers
o guests
• All these components are interchangable
o mixed-and-matched
o choose the best OS to support your apps and hardware
• Strong isolation between these components
o especially with modern hardware support
o domains can be restarted as needed without taking out
system
• Good scaling
o Use your big machine without big domains
16. Different Use Cases
• Servers
o the old reliable: server consolidation
o standard open-source Xen
• Cloud
o efficient management of images
o rapid instancing
o Xen Cloud Platform (about 80% of XenServer)
• Hosted desktops
o much the same as servers, except
o need lots of magic goo to make it efficient
Lots of Citrix products
17. More Use Cases
• Client virtualization
o Personal domain vs. Corporate locked-down domain
o needs to work on modern laptops/desktops
o needs most up-to-date driver support
o XenClient (free, mostly open source)
• Secure Applications
o launch individual apps and app clusters in their own
domains
o for example:
random website browsing
online banking
shopping
...
o Invisible Things Labs' Qubes-OS: http://qubes-os.org/
18. More Info
● Web
● Home Page (http://www.xen.org)
● Documents
● Why Xen? - What is Xen? - How Does Xen Work?
● Support
● IRC ##xen and #xen-api (XCP Project)
● Xen Mailing Lists (http://lists.xensource.com)
Thanks to Jeremy Fitzhardinge for the creation of these excellent slides on Xen and
other virtualization alternatives
