Why Xen?August 2010

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 paravirtualizationo 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

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 Citrixo Oracleo Novello etc

• They add support and advanced features

Xen Compared to...

• Xen has a "thin hypervisor" modelo hypervisor has no device drivers, very little smartso is just there to keep "domains" isolatedo ~2MB executableo relies on service domains to do lots of its work

• VMware ESXi is similaro but also has device driverso and base of management stacko hardware support depends on VMware writing drivers

• Hyper-V very similar to Xeno Designers explicitly modelled it after Xen

• KVM has a very different modelo Linux kernel as hypervisor

Xen Architecture

Hyper-V Architecture

ESXi Architecture

KVM Architecture

Let's look at that again...

Let's look at that again...

Let's look at that again...

Let's look at that again...

Let's look at that again...

Let's look at that again...

So what did all that mean?

• Xen keeps the hypervisor job separate from:o management OSo management stacko device driverso guests

• All these components are interchangableo mixed-and-matchedo choose the best OS to support your apps and hardware

• Strong isolation between these componentso especially with modern hardware supporto domains can be restarted as needed without taking out

system• Good scaling

o Use your big machine without big domains

Different Use Cases• Servers

o the old reliable: server consolidationo standard open-source Xen

• Cloudo efficient management of imageso rapid instancingo Xen Cloud Platform (about 80% of XenServer)

• Hosted desktopso much the same as servers, excepto need lots of magic goo to make it efficient

Lots of Citrix products

More Use Cases• Client virtualization

o Personal domain vs. Corporate locked-down domaino needs to work on modern laptops/desktopso needs most up-to-date driver supporto XenClient (free, mostly open source)

• Secure Applicationso launch individual apps and app clusters in their own

domainso for example:

random website browsing online banking shopping ...

o Invisible Things Labs' Qubes-OS: http://qubes-os.org/

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