Finding out total and free disk space in .NET

How about this link from MSDN that uses the System.IO.DriveInfo class?

Not really a C# example but may give you a hint - a VB.NET function returning both amount of free and total space on drive (in bytes) along specified path. Works for UNC paths as well, unlike System.IO.DriveInfo.

VB.NET:

<DllImport("kernel32.dll", SetLastError:=True, CharSet:=CharSet.Auto)> _
Private Shared Function GetDiskFreeSpaceEx(lpDirectoryName As String, ByRef lpFreeBytesAvailable As ULong, ByRef lpTotalNumberOfBytes As ULong, ByRef lpTotalNumberOfFreeBytes As ULong) As <MarshalAs(UnmanagedType.Bool)> Boolean
End Function

Public Shared Function GetDriveSpace(folderName As String, ByRef freespace As ULong, ByRef totalspace As ULong) As Boolean
    If Not String.IsNullOrEmpty(folderName) Then
        If Not folderName.EndsWith("\") Then
            folderName += "\"
        End If

        Dim free As ULong = 0, total As ULong = 0, dummy2 As ULong = 0
        If GetDiskFreeSpaceEx(folderName, free, total, dummy2) Then
            freespace = free
            totalspace = total
            Return True
        End If
    End If
End Function

This may not be what you want, but I'm trying to help, and it has the bonus of slightly secure erasing the free space of your drive.

public static string DriveSizeAvailable(string path)
{
    long count = 0;
    byte toWrite = 1;
    try
    {
        using (StreamWriter writer = new StreamWriter(path))
        {
            while (true)
            {
                writer.Write(toWrite);
                count++;
            }
        }
    }
    catch (IOException)
    {                
    }

    return string.Format("There used to be {0} bytes available on drive {1}.", count, path);
}

public static string DriveSizeTotal(string path)
{
    DeleteAllFiles(path);
    int sizeAvailable = GetAvailableSize(path);
    return string.Format("Drive {0} will hold a total of {1} bytes.", path, sizeAvailable);
}

You can use GetDiskFreeSpaceEx from kernel32.dll which works with UNC-paths and drives. All you need to do is include a DllImport (see link for an example).