The Azure bill does not care about how much is actually stored on the disk, they just bill based of the Reservation selected when creating the disk. For example, if you were to sum the quantity for a particular disk it would equal one:

 "metername": "P1 LRS Disk", "unitofmeasure": "1/Month", "quantity": 0.033336000000000005, "effectiveprice": 0.5239, "costinbillingcurrency": 0.0174647304,

That is because they are charging you for 1 P1 LRS Disk a month. The azure docs define a P1 LRS disk as 4 GiB; however, that information is not present in their billing structure.As for what we do today, we charge PVs that may only be using 2GiB of the disk the full cost of the disk.

We need a way to retrieve the Azure storage capacity so that we can calculate how much of the disk was unused as an Unattributed Storage cost.