#Xen

Today saw the release of Xen 4.1. Major changes include support for greater than 255 CPUs, a new credit scheduler and CPU pools.

However, the most significant change to those that use Xen will be the new XL toolstack which replaces XM/XEND and will ultimately replace xcp’s xapi and libvirt.

For distros that don’t support XEN compatible installers the easiest way to create a PV (ParaVirtual) DOMU is to install as a HVM (see my other article entry for this) ad then once installed, convert it to a PV DOMU.

There are several reasons why you might want to go with PV instead of HVM. The main two that spring to mind are PV’s offer better performance/lower overhead and PV DOMU’s allow PCI passthrough. Although apparently XEN 3.4 can now do PCI passthrough with HVM, as long as you have an Intel chip with vt-d.

This article will start off where my previous “Installing a XEN hvm DOMU” left off…

For this to work your CPU and motherboard needs to support vt (intel) or amd-v. You can check this by looking at the flags in /proc/cpuinfo. Your looking for either vmx or svm on the flags line.

If you’re doing this from your DOM0 then these flags may not actually show up. Instead type xm info and look for ‘hvm’ on the virt_caps line.

For my hvm install, i’ll be installing Ubuntu 9.04 Desktop Linux.
I have copied the live CD ISO onto my XEN DOM0 and will be installing directly from the iso rather than burning the CD. I have also created a 10GB LVM logical volume to act as the disk for my new DOMU.

If you’ve followed my guide to installing xen from source then you might now be wondering how to create your first VM.
This guide will show you how to manually create and install a VM (known as a DOMU instance in Xen) without any additional tools such as virt-manager, virt-install or virsh. These tools can help the novice, but are quite limiting when it comes to the advance features of xen.

For this example I’ll be installing CentOS5, but this should work for any red-hat based distro (please note there is a bug in fedora10 that stops it booting under xen). This example also uses the paravirtual kernel so it will work even if your CPU does not support AMD-V or intel-VT.

Right, down to business. The first thing we need to do is create a file to user as the hard disk for the DOMU. There are other options for providing hard disks to a DOMU, and I’ll cover some of them in a later guide but for this install I’ll be using a file.

The command below will create an 8GB file that will be used as an 8GB drive. The whole file will be written to disk in one go so may take a short while to complete.
dd if=/dev/zero of=/xenimages/test01/disk1.img oflag=direct bs=1M count=8192

This is how I built my Xen server.

First install Debian 5.0 (Lenny). This should also work on 4 (Etch) too.

Everything is done on the command line as root.

To build Xen from source you’ll need as fair number of dependencies. The easiest way to install them is by using the apt-get install command as below:
apt-get install bcc bin86 gawk bridge-utils iproute libcurl3 libcurl4-openssl-dev bzip2 module-init-tools transfig tgif texinfo pciutils-dev mercurial build-essential make gcc libc6-dev zlib1g-dev python python-dev python-twisted libncurses5-dev patch libvncserver-dev libsdl-dev libjpeg62-dev

If you installed the 64bit version of Debian then you’ll also need gcc-multilib for the compile to work:
apt-get install gcc-multilib