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FSCTL_GET_COMPRESSION IOCTL (winioctl.h)

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Retrieves the current compression state of a file or directory on a volume whose file system supports per-stream compression.

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,             // handle to file
  FSCTL_GET_COMPRESSION,        // dwIoControlCode
  NULL,                         // lpInBuffer 
  0,                            // nInBufferSize
  (LPVOID) lpOutBuffer,         // output buffer
  (DWORD) nOutBufferSize,       // size of output buffer
  (LPDWORD) lpBytesReturned,    // number of bytes returned
  (LPOVERLAPPED) lpOverlapped   // OVERLAPPED structure
);

Remarks

The LZNT1 compression algorithm is the only compression algorithm implemented.

COMPRESSION_FORMAT_DEFAULT is not a compression state so it is not included in the table under the lpOutBuffer parameter. This value is only used with the FSCTL_SET_COMPRESSION control code.

If the file system of the volume containing the specified file or directory does not support per-file or per-directory compression, the operation fails.

You can set the compression state of a file or directory by using the FSCTL_SET_COMPRESSION control code. You can also compress or uncompress a file using this control code.

You can retrieve the compression attribute of a file or directory by calling the GetFileAttributes function. The compression attribute indicates whether a file or directory is compressed. The compression state indicates whether a file or directory is compressed, and, if it is, the format of the compressed data.

In Windows 8 and Windows Server 2012, this code is supported by the following technologies.

Technology Supported
Server Message Block (SMB) 3.0 protocol Yes
SMB 3.0 Transparent Failover (TFO) No
SMB 3.0 with Scale-out File Shares (SO) No
Cluster Shared Volume File System (CsvFS) Yes
Resilient File System (ReFS) No

SMB 3.0 Transparent Failover and Scale-Out do not support NTFS compressed files. The FSCTL call is not blocked, but unsupported.

Requirements

Requirement Value
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Header winioctl.h (include Windows.h)

See also