We currently am using OpManager to produce disk utilization reports for several of our servers but we have noticed a few discrepancies from report to report.

I have a Top 25 Utilization report and I also run a Disk Space Available report.  For one of our servers, the Utilization report shows 86% used space on the C: drive, while the Disk Space Available report is showing 90%.  Why would it reporting two different numbers for the same drive?