Increases the size of a mounted volume.

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

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



A handle to the volume. To retrieve a volume handle, call the CreateFile function. Only administrators can open volume handles.


The control code for the operation. Use FSCTL_EXTEND_VOLUME for this operation.


A pointer to a LONGLONG value that specifies the total size of the volume, in sectors.


The size of the input buffer.


Not used with this operation; set to NULL.


Not used with this operation; set to zero.


A pointer to a variable that receives the size of the data stored in the output buffer, in bytes.

If lpOverlapped is NULL, lpBytesReturned cannot be NULL. Even when an operation returns no output data and lpOutBuffer is NULL, DeviceIoControl makes use of lpBytesReturned. After such an operation, the value of lpBytesReturned is meaningless.

If lpOverlapped is not NULL, lpBytesReturned can be NULL. If this parameter is not NULL and the operation returns data, lpBytesReturned is meaningless until the overlapped operation has completed. To retrieve the number of bytes returned, call GetOverlappedResult. If hDevice is associated with an I/O completion port, you can retrieve the number of bytes returned by calling GetQueuedCompletionStatus.


A pointer to an OVERLAPPED structure.

If hDevice was opened without specifying FILE_FLAG_OVERLAPPED, lpOverlapped is ignored.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, the operation is performed as an overlapped (asynchronous) operation. In this case, lpOverlapped must point to a valid OVERLAPPED structure that contains a handle to an event object. Otherwise, the function fails in unpredictable ways.

For overlapped operations, DeviceIoControl returns immediately, and the event object is signaled when the operation has been completed. Otherwise, the function does not return until the operation has been completed or an error occurs.

Return value

If the operation completes successfully, DeviceIoControl returns a nonzero value.

If the operation fails or is pending, DeviceIoControl returns zero. To get extended error information, call GetLastError.


This control code is supported on NTFS, RAW, and ReFS file systems.

This control code cannot be used to reduce the size of a volume. The new volume size must be at least one cluster larger than the previous volume size. The underlying partition must have enough sectors to contain the extended volume. If not, IOCTL_DISK_GROW_PARTITION can be used if the underlying device has enough space available.

You can extend a live volume, and the volume can be open for sharing during the extend operation.

You do not need to lock a volume that you are extending, nor do you need to shut down other applications or services during the extend operation.

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


Server Message Block (SMB) 3.0 protocol


SMB 3.0 Transparent Failover (TFO)


SMB 3.0 with Scale-out File Shares (SO)


Cluster Shared Volume File System (CsvFS)


Resilient File System (ReFS)




Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]


WinIoCtl.h (include Windows.h)

See also

Volume Management Control Codes