Unable to collect VM disk.usage.average metrics via PerfManager

[madhurish]

I want to use the performance manager to get the disk.usage.average values at 30 min intervals over a period of 7 days, as it is a level 1 call, I should be able to get the details, however, I'm not able to get those details. I'm getting an empty list, Could someone direct me to some code samples to get vm disk performance data?