除非缓冲区大小是512的倍数，否则读取NTFS卷根目录失败

我在玩MFT，首先使用p/Invoke调用读取C:驱动器的根目录。使用下面的代码，如果缓冲区大小是512的倍数，我会得到预期的结果，但如果不是这样，则读取失败，返回ERROR_INVALID_PARAMETER。这与集群大小有关吗？这似乎不太可能，因为我的集群大小为4k字节。很明显，我可以只使用512的倍数，但在我看来，这可能是不可移植的，当然我想理解为什么会这样

    public void Test()
    {
        string driveRoot = @"''.'" + "C:";
        IntPtr hRoot = MFT.CreateFile(
            driveRoot,
            MFT.GENERIC_READ | MFT.GENERIC_WRITE,
            MFT.FILE_SHARE_READ | MFT.FILE_SHARE_WRITE,
            IntPtr.Zero,
            MFT.OPEN_EXISTING,
            MFT.FILE_ATTRIBUTE_NORMAL,
            IntPtr.Zero);
        if (hRoot.ToInt32() == MFT.INVALID_HANDLE_VALUE)
            throw new IOException(string.Format("CreateFile() returned invalid handle [Win32 error {0}]", Marshal.GetLastWin32Error()));
        // TODO why does this fail unless buffer size is a multiple of 512? Is it to do with cluster size?
        UInt32 numBytesToRead = 512;
        byte[] buffer = new byte[numBytesToRead];
        if (ReadFileFromHandleSync(hRoot, buffer, numBytesToRead))
            Debug.WriteLine("OK " + i);
    }

    public bool ReadFileFromHandleSync(IntPtr handle, byte[] buffer, UInt32 numBytesToRead)
    {
        UInt32 numBytesRead;
        NativeOverlapped overlapped = new NativeOverlapped();
        bool readOK = ReadFile(handle, buffer, numBytesToRead, out numBytesRead, ref overlapped);
        return readOK;
    }
}