Free Virtualization Introduction

Xen on Linux is usable out of the box now. If you download CentOS 5.1 (or later I would guess), you can setup virtualization during install.

Virtualization lets you run multiple instances of an operating system and applications on one piece of hardware. You can imagine or read on the net why that would be useful.

Some terms to translate for those familiar with VMWare or Parallels style terminology:

Host OS: VMWare Server (not ESX) uses an operating system (windows or linux) as a host, ESX is the host, and Parallels uses OS X. With Xen virtualization this roughly corresponds to Domain0. Domain0 has unlimited privileges.

Guest OS: You can run windows, linux or other operating systems under VMWare or Parallels. On Xen the guest OS is known as a DomU (domain U), which has direct access to hardware. This domain has limited resources (ram and processors as configured), by default it has no access to hardware.

Paravirtualization vs. fully virtualized-

paravirtualization uses software to allow virtualization. Under CentOS 5, the paravirtualizable guest operating systems are basically linux, linux and linux. Native virtualization uses processor extensions so you need a recent Intel processor that supports or a AMD that supports AMD-V extensions. The extensions aren't very common outside of server class chips (Xeon and Opteron). Here is how to tell if you have the extensions:

egrep '^flags.*(vmx|svm)' /proc/cpuinfo

If you don't have a lines of output with vmx or svm in them, you don't have the extensions.

P2V: Physical to Virtual. How to import physical servers (usually old), to a virtual machine, which can save you time and money and get you out of supporting old and busted servers. There are some pay tools for P2V for Xen and Linux. But here is a pretty good free one:

http://et.redhat.com/~rjones/virt-p2v/

That is it for the intro. More tomorrow with specific examples.