function _GetErrorMsg(ecode: Cardinal): string;
var
  Buf: array [0 .. 1024] of char;
begin
  SetString(Result, Buf, FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, nil, ecode, 0, @Buf, sizeOf(Buf), nil));
  Result := StringReplace(Result, #13#10, '', [rfReplaceAll]);
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  filename: String;
  hfile: THandle;
  buffer: TBytes;
  i: integer;
  blocksize: integer;
  bytesWritten: Cardinal;
  res: Boolean;
begin
  filename := 'D:\PR\de\data.txt';
  hfile := CreateFile(pchar(filename), GENERIC_WRITE, 0, nil, CREATE_ALWAYS, FILE_FLAG_WRITE_THROUGH, 0);
  if hfile = INVALID_HANDLE_VALUE then
  begin
    ShowMessage(_GetErrorMsg(GetLastError));
    exit;
  end;
  blocksize := 32000;
  Randomize;
  SetLength(buffer, blocksize);
  for i := 1 to blocksize do
  begin
    buffer[i - 1] := Random(100) + 100;
  end;
  for i := 1 to 40000 do
  begin
    res := WriteFile(hfile, buffer[0], blocksize, bytesWritten, nil);
    if res = false then
    begin
      ShowMessage(_GetErrorMsg(GetLastError));
      exit;
    end;
  end;
  FlushFileBuffers(hfile);
  CloseHandle(hfile);
end;