Disk usage discrepancy?

You need to search for errors related to a database or a filewalker. Depending on what error do you have we can suggest a solution.
Restarting the computer or reinstalling the node likely will not help, because likely you need to optimize the disk subsystem instead.
Since you use Windows and NTFS, you need to do:

  1. Check and fix errors on the disk
  2. NTFS Disable 8dot3name
  3. [Solved] Win10 20GB Ram Usage - #17 by arrogantrabbit
  4. defragment the disk
  5. If you have a managed UPS, then you may also enable a write cache for the disk (both checkboxes), however, if you do not have a managed UPS, you should not enable it (especially the second checkbox).

The next step would be to search errors in your logs with PowerShell:

sls error "$env:ProgramFiles\Storj\Storage Node\storagenode.log" | sls "database|used-space" | select -last 10