The Disk Usage metric in the Disk Usage Report (Reports > Azure Usage > Disk) represents the average Disk Hours # for the chosen interval.
The following article provides insights on what the units of measurement are and how they calculated:
https://support.cloudhealthtech.com/hc/en-us/articles/360035267512-What-does-Disk-Usage-metrics-represent-in-the-Azure-Disk-Usage-Report-
The storage GBs filter included represents the disk storage allocated with respect to desired time interval.
NOTE: The platform currently pulls disk size allocated but not the actual disk space used.