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


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.

Technology Supported
Server Message Block (SMB) 3.0 protocol No
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) Yes


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