Meg egy másik lehetőség:

Private Declare Function GetDiskFreeSpace Lib "kernel32" Alias "GetDiskFreeSpaceA" (ByVal lpRootPathName As String, lpSectorsPerCluster As Long, lpBytesPerSector As Long, lpNumberOfFreeClusters As Long, lpTtoalNumberOfClusters As Long) As Long

Sub DiskInfo()
Dim Sectors As Long, Bytes As Long, FreeC As Long, TotalC As Long, TotalGB As Single, FreeGB As Long
GetDiskFreeSpace "C:", Sectors, Bytes, FreeC, TotalC
Debug.Print " Drive C:"
TotalGB = TotalC / 1024 * Sectors / 1024 * Bytes / 1024
Debug.Print " Total space: " & TotalGB & "GB"
FreeGB = FreeC& / 1024 * Sectors / 1024 * Bytes / 1024
Debug.Print " Free space: " & FreeGB & "GB"
End Sub

(Forrás)