Is volume compressed?

[Der schöne Günther]

I might be wrong, but I believe there is no clear indication if a volume is either compressed or not compressed at all. We're talking about NTFS, right? I think the FILE_VOLUME_IS_COMPRESSED flag still hails from the time of the FAT file system. Back then, a volume was either entirely compressed ("double space volume") or no compression at all was taking place.

Take a look: Set a volume of yours to "compressed". Create some folders, they're all blue (compressed). Now set a folder to "uncompressed". Your volume will still state "compressed". I believe "volume compression" only means "Default setting for compressing content or not".

Keeping this in mind, this is what I baked together:

Delphi-Quellcode:

procedure TForm18.checkCompression();
const
   // According to http://www.swissdelphicenter.ch/en/showcode.php?id=1053
   COMPRESSION_FORMAT_NONE = 0;
   COMPRESSION_FORMAT_LZNT1 = 2;
   COMPRESSION_FORMAT_DEFAULT = 1;
var
   fileHandle: THandle;
   outBuffer: ^USHORT;
   bufferLength: DWORD;
begin


   // Fetch Handle
   fileHandle := CreateFile(
      'F:\.',
      GENERIC_READ,
      FILE_SHARE_READ,
      nil,
      OPEN_EXISTING,
      FILE_ATTRIBUTE_NORMAL or FILE_FLAG_BACKUP_SEMANTICS,
      0
   );

   if (fileHandle = INVALID_HANDLE_VALUE) then raise Exception.Create('CreateFile Failed');

   // Init Buffer
   New(outBuffer);

   if not DeviceIoControl(
      fileHandle,
      FSCTL_GET_COMPRESSION,
      nil,
      0,
      outBuffer,
      SizeOf(outBuffer),
      bufferLength,
      nil
   ) then raise Exception.Create('DeviceIoControl failed');

   if (outBuffer^ and COMPRESSION_FORMAT_LZNT1) <> 0 then
      ShowMessage('it is compressed');


end;