Xen

is now

Donald Gordon

don@dis.org.nz
Hastily-writing-up MSc Student, VUW

Overview

• Virtualisation
• Xen
• Using Xen

Virtualisation

• One physical machine
• Several smaller virtual machines
• VMs appear like real physical machines
• Share disk, CPU, network, ...
• Not emulation — partitioning
• Hard on x86
• This is not new
  • VM
  • MacOnLinux (PowerPC)
  • kqemu
  • VMWare

Why?

• Virtual hosting
• Server sharing
• Server consolidation: space, power, hardware savings
• Low deployment time

Paravirtualisation

• Virtualisation is hard on x86
• Hardware emulation is slow
• Why does a virtual machine have to provide an identical environment to a physical machine?
• Make available an API that provides operations similar to those that are hard to virtualise
• Throw in some virtual I/O devices
• Modify guest OS kernels
  • Like a386, User Mode Linux

Xen

• Paravirtualisation on x86, AMD64
• Developed by University of Cambridge's Systems Research Group
• Free, open source
• Good performance
• Migration
• Kernel patches
  • Linux
  • NetBSD
  • FreeBSD, Plan 9 in the works

What about Windows?

• Windows XP patches developed, but unavailable
• CPU manufacturers to the rescue!
• AMD Pacifica, Intel Vanderpool
• Xen3 supports these

Core Concepts

• Domains
• Virtual network interfaces
• Virtual block devices
  • Use LVM
  • I mean it
• Real PCI devices

make world

• If you want to configure your kernels, best to compile from source
• Guest VMs need no tools installed
• Source is at the hard-to-find http://wiki.xensource.com/xenwiki/XenDownloads

make world
cd linux-*-xen0; make ARCH=xen menuconfig; cd ..
cd linux-*-xenU; make ARCH=xen menuconfig; cd ..
make
cd dist; checkinstall ./install.sh
$EDITOR /boot/grub/menu.lst
reboot

Boot Process

• GRUB
• Xen hypervisor
• Dom0
• init scripts bring up more domains

$EDITOR /etc/xen/auto/vmname

kernel = "/boot/vmlinuz-2.6.11-xenU"
memory = 256
# name must be unique
name = "vmname"
nics = 1
vif = [ 'mac=00:60:b0:28:78:84, bridge=xen-cust' ]
disk = ['phy:vg0/vmname_root,sda1,w',
        'phy:vg0/vmname_swap,sda2,w',
        'phy:vg0/modules,sda3,r']
root = "/dev/sda1 ro"

• xm create -f /etc/xen/auto/vmname
• xm console vmname

A running system

root@greebo:~# xm list
Name              Id  Mem(MB)  CPU  State  Time(s)  Console
Domain-0           0       59    0  r----  11015.9
hex                1      255    0  -b---  17024.3    9601
tepidmail          2      127    0  -b---   3123.5    9602
thinfaw            3       63    0  -b---  14682.4    9603
visit              4      255    0  -b---   3658.6    9604
william            5      127    0  -b---   1246.1    9605
root@greebo:~#

• 1.38% cpu utilisation over 42 days
• Much more reliable than the old machines it replaced

Questions?

• I must have missed something

Resources

• http://www.cl.cam.ac.uk/Research/SRG/netos/xen/
• http://www.cl.cam.ac.uk/Research/SRG/netos/xen/readmes/user/user.html
• Binaries: http://www.xensource.com/xen/downloads/
• Source: http://wiki.xensource.com/xenwiki/XenDownloads
• This talk: http://www.dis.org.nz/talks/xen/