The influence of the virtualized I/O controller
Another important thing to check is the influence of the virtualized I/O controller that is presented to the guest. KVM let you use not only the default IDE virtual controller, but also a new, paravirtualized I/O controller called VirtIO. This virtualized controller promise better speed and less CPU usage.
How it affect the results?
As you can see, the write-through scenario is the most affected one, while with the no-caching and write-back policies it has a lesser effect.
This does not means that the VirtIO is an unimportant project: the scope of this test was only to be sure that it don't comport any I/O slowness. In a following article I will analyze this very promising driver in a much more complete manner.