无法在munin中获取IO服务时间的图表

I am implementing munin on my ec2 ubuntu 10.04 instance I was not able to fetch graph for IO stats but I figured out the problem and IO stats are working fine. But still I am not able to fetch the graphs for IO service Time, which is one of the very important parameter. Kindly help me.I am implementing munin on my ec2 ubuntu 10.04