Manage Your Server: Disk I/O Viewer
You can use this option to view reports of disk I/O tests which were performed earlier.
If no tests were run yet, there will be no reports to show.
First run the performance monitor, then you will be able to choose a report to display.
Finally, you can view the generated report.
Notice how you can hover with the mouse over a point on the graph and get the actual numbers for that time.