This is very, very, very, very, very, very, very, very, very (inhale, exhale) very, very, very, trivial stuff, but for those who find it useful, here goes (phew!)
The default Hardware Inventory setting collects data from the Win32_LogicalDisk WMI class, but it does not (by default) capture the FreeSpace property. Why does this matter? Well, when certain customers I know have removed all but one hair on their head trying to figure out why they can’t get a Query or Report to find those with “less than _” free space, they figure out that it’s just a checkbox that needs checking.
The first sign might be a null value for the “Free Space (MB)” property when viewing a device in the Resource Explorer.
To address, select Administration, then Client Settings. If you have more than the standard “Default Client Settings” object, choose the appropriate one (or choose all of them, whatever makes you happy), and open the Properties for that object.
Within the Properties form, select Hardware Inventory, and then click the “Set Classes…” button…
Scroll down to the “Logical Disk (SMS_LogicalDisk)” entry, and expand its properties list. Then check the box to enable “Free Space (MB)”. Notice that the image below shows the default state of that seting (unchecked).
The inventory data should begin populating as soon as clients obtain the updated policy and run the next inventory scan after that. You can force that from the Control Panel applet, or using your favorite Right-Click tools add-in from the console, or via a script, or via two sticks and some mud with a voodoo dance. Whatever works for you.
I hope this was helpful.