random notes on setting up KVM + libvirt + virtio

This is a collection of notes I took while setting up a virtual machine host which has several guest virtual machines running on Ubuntu 8.10.

1) Create a logical volume to install the guest

$ sudo lvcreate -v -n phq_mail -L 80G vg0 /dev/md1
    Setting logging type to disk
    Finding volume group \"vg0\"
    Creating directory \"/etc/lvm/archive\"
    Archiving volume group \"vg0\" metadata (seqno 6).
    Creating logical volume phq_mail
    Creating volume group backup \"/etc/lvm/backup/vg0\" (seqno 7).
    Found volume group \"vg0\"
    Creating vg0-phq_mail
    Loading vg0-phq_mail table
    Resuming vg0-phq_mail (254:5)
    Clearing start of logical volume \"phq_mail\"
    Creating volume group backup \"/etc/lvm/backup/vg0\" (seqno 7).
  Logical volume \"phq_mail\" created

Remember you can view all your logical volumes using lvdisplay

2) Creating a network segment to separate the servers from the rest of the network (the clients will use routing through the host to access the server).

$ vim ~/pofhq-servers.xml
	
<network>
  <name>default</name>
  <uuid>e81218cf-6d5a-4a6f-8af8-b2d5b77947be</uuid>
  <bridge name=\"virbr%d\" />
  <forward/>
  <ip address=\"192.168.25.1\" netmask=\"255.255.255.0\">
    <dhcp>
      <range start=\"192.168.25.2\" end=\"192.168.25.30\" />
    </dhcp>
  </ip>
</network>
	
$ virsh net-define pofhq-servers.xml
Network pofhq-servers defined from pofhq-servers.xml
	
$ virsh net-create pofhq-servers.xml
Network pofhq-servers created from pofhq-servers.xml
	
$ virsh net-autostart pofhq-servers
Network pofhq-servers marked as autostarted
	
$ rm ~/pofhq-servers.xml

This will create the file pofhq-servers.xml into /etc/libvirt/qemu/networks and link it to autostart folder.

Optionally, if you don’t want to use the ‘default’ network segment, you can delete it:

$ virsh net-undefine default
$ virsh net-destroy default

This will automatically delete de default-network.xml file (and autostart symlink if present) on /etc/libvirt/qemu/networks.

3) Installing the guest operating system using virtio for best virtual machine network and disk performance

We will start by letting virt-install create the default VM template for us:

$ sudo virt-install -n phq_mail -r 1024 -f /dev/vg0/phq_mail -c ubuntu-server.iso --accelerate --vnc --noautoconsole -v
Starting install...
Creating domain...                                                 0 B 00:00
Domain installation still in progress.  You can reconnect to
the console to complete the installation process.

Right after this, we will stop the VM and edit it’s configuration manually:

$ virsh shutdown phq_mail
$ virsh dumpxml phq_mail > phq_mail.xml
$ virsh undefine phq_mail
$ virsh destroy phq_mail
$ vim phq_mail.xml

Make the following modifications:

  • Boot from CD:
  <os>
    <type>hvm</type>
    <boot dev='cdrom'/>
  </os>
	
    <disk type='file' device='cdrom'>
      <source file='/home/pau/ubuntu-8.10-server-i386.iso'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
    </disk>
  • Use virtio for the hard disk:
    <disk type='block' device='disk'>
      <source dev='/dev/vg0/phq_mail'/>
      <target dev='vda' bus='virtio'/>
    </disk>
  • Use virtio for the network:
    <interface type='network'>
      <mac address='00:16:36:7a:7b:7c'/>
      <source network='pofhq-servers'/>
      <model type='virtio'/>
    </interface>

Save the file, and create again the virtual machine with the new config:

$ virsh define phq_mail.xml
Connecting to uri: qemu:///system
Domain phq_mail defined from phq_mail.xml
	
$ virsh create phq_mail.xml
Connecting to uri: qemu:///system
Domain phq_mail created from phq_mail.xml
	
$ virsh autostart phq_mail
Connecting to uri: qemu:///system
Domain phq_mail marked as autostarted

Install normally, and then change the boot option to ‘hd’ to boot from normal hard disk again when installation has been finished (if needed, use shutdown/undefine/destroy and define/create/autostart again after finishing the installation).

4) If the guest VM you have installed is Ubuntu, remember to install acpid, for the VM to shutdown cleanly.

5) Useful documentation:

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