Get free space

gistfile1.cs

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
        [return: MarshalAs(UnmanagedType.Bool)]
        static extern bool GetDiskFreeSpaceEx(string lpDirectoryName,
           out ulong lpFreeBytesAvailable,
           out ulong lpTotalNumberOfBytes,
           out ulong lpTotalNumberOfFreeBytes);
           
ulong FreeBytesAvailable;
ulong TotalNumberOfBytes;
ulong TotalNumberOfFreeBytes;

bool success = GetDiskFreeSpaceEx(path,
                                  out FreeBytesAvailable,
                                  out TotalNumberOfBytes,
                                  out TotalNumberOfFreeBytes);