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3.3. Post-installation host configuration

This section covers the post-installation configuration processes required to utilize the para-virtualized drivers. Para-virtualized drivers must be installed on the guest before commencing this section.
Network devices available to guests automatically use the para-virtualized drivers when the guests are rebooted after installation of the drivers. Adding network devices requires special configuration steps, refer to Section 4.2, “Adding para-virtualized network devices”.
Block devices require additional configuration.
Block device configuration

This section covers the procedure for adding and modifying disk entries to enable the para-virtualized drivers. Each guest requires modification in order to utilize the drivers.

Para-virtualized drivers cannot be used for the disk containing the Windows system files. Only secondary disks can be used with the para-virtualized drivers at this time.

Warning

Only make changes to the configuration files in the /etc/xen directory with the libvirt based tools, virsh and virt-manager. Manually editing configuration files in the /etc/xen directory is not recommended and could render your guests inoperable.
Use virsh dumpxml to export the configuration of the virtual machine. 
# virsh dumpxml virt-machine-name > guest.xml
Update the guest configuration to enable the para-virtualized drivers. Red Hat Enterprise Linux 5.2 automatically enables para-virtualized network drivers. Only the block and disk device drivers must be updated.
The guest.xml file locate the section containing the disk configuration should resemble this example. This example uses a hard disk partition called /dev/hda6. 
<disk type='file' device='disk'>
  <driver name='file'/>
  <source file='/var/lib/xen/images/disk1.img'/>
  <target dev='hda'/>
</disk>
<disk type='file' device='disk'>
  <driver name='file'/>
  <source file='/dev/hda6'/>
  <target dev='hdb'/>
</disk>
In this example, the secondary disk updated to use the para-virtualized driver. Change the driver from “file” to “tap:aio” and change the target device from “hdb” to “xvdb”. 
<disk type='file' device='disk'>
  <driver name='file'/>
  <source file='/var/lib/xen/images/disk1.img'/>
  <target dev='hda'/>
</disk>
<disk type='file' device='disk'>
  <driver name='tap' type='aio'/>
  <source file='/dev/hda6'/>
  <target dev='xvdb'/>
</disk>
Redefine the guest using the updated guest configuration file, guest.xml. 
# virsh define guest.xml
The guest can now be restarted with virt-manager or virsh. To restart a guest named virt-machine-name: 
# virsh reboot virt-machine-name