RHEL 6 Virtualization - 11.3. Using KVM para-virtualized drivers for existing devices

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11.3. Using KVM para-virtualized drivers for existing devices

You can modify an existing hard disk device attached to the guest to use the virtio driver instead of the virtualized IDE driver. This example edits libvirt configuration files. Alternatively, virt-manager, virsh attach-disk or virsh attach-interface can add a new device using the para-virtualized drivers Section 11.4, “Using KVM para-virtualized drivers for new devices”. Note that the guest does not need to be shut down to perform these steps, however the change will not be applied until the guest is completely shut down and rebooted.

Run the virsh edit <guestname> command to edit the XML configuration file for your device. For example, virsh edit guest1. The configuration files are located in /etc/libvirt/qemu.
Below is a file-based block device using the virtualized IDE driver. This is a typical entry for a virtualized guest not using the para-virtualized drivers.
```
<disk type='file' device='disk'>
   <source file='/var/lib/libvirt/images/disk1.img'/>
   <target dev='hda' bus='ide'/>
</disk>
```
Change the entry to use the para-virtualized device by modifying the bus= entry to virtio. Note that if the disk was previously IDE it will have a target similar to hda, hdb, or hdc and so on. When changing to bus=virtio the target needs to be changed to vda, vdb, or vdc accordingly.
```
<disk type='file' device='disk'>
   <source file='/var/lib/libvirt/images/disk1.img'/>
   <target dev='vda' bus='virtio'/>
</disk>
```
Remove the address tag inside the disk tags. This must be done for this procedure to work. Libvirt will regenerate the address tag appropriately the next time the guest is started.

Please refer to the libvirt wiki: https://wiki.libvirt.org/page/Virtio for more details on using Virtio.