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FSCTL_LOCK_VOLUME control code

Locks a volume if it is not in use. A locked volume can be accessed only through handles to the file object (*hDevice) that locks the volume. For more information, see the Remarks section.

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

BOOL DeviceIoControl(
  (HANDLE) hDevice,            // handle to a volume
  (DWORD) FSCTL_LOCK_VOLUME,   // dwIoControlCode
  NULL,                        // lpInBuffer
  0,                           // nInBufferSize
  NULL,                        // lpOutBuffer
  0,                           // nOutBufferSize
  (LPDWORD) lpBytesReturned,   // number of bytes returned
  (LPOVERLAPPED) lpOverlapped  // OVERLAPPED structure



A handle to the volume to be locked. To retrieve a device handle, call the CreateFile function.


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


Not used with this operation; set to NULL.


Not used with this operation; set to zero.


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.


The hDevice handle passed to DeviceIoControl must be a handle to a volume, opened for direct access. To retrieve this handle, call CreateFile with the lpFileName parameter set to a string of the following form:


where X is a hard-drive partition letter, floppy disk drive, or CD-ROM drive. The application must also specify the FILE_SHARE_READ and FILE_SHARE_WRITE flags in the dwShareMode parameter of CreateFile.

If the specified volume is a system volume or contains a page file, the operation fails.

If there are any open files on the volume, this operation will fail. Conversely, success of this operation indicates there are no open files.

This operation is useful for applications that need exclusive access to a volume for a period of time—for example, disk utility and backup programs.

A locked volume remains locked until one of the following occurs:

  • The application uses the FSCTL_UNLOCK_VOLUME control code to unlock the volume.
  • The handle closes, either directly through CloseHandle, or indirectly when a process terminates.

The system flushes all cached data to the volume before locking it. For example, any data held in a lazy-write cache is written to the volume.

The NTFS file system treats a locked volume as a dismounted volume. The FSCTL_DISMOUNT_VOLUME control code functions similarly but does not check for open files before dismounting. Note that without a successful lock operation, a dismounted volume may be remounted by any process at any time. This would not be an ideal state for performing a volume backup, for example.

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)

See comment


On CsvFs Lock Volume, PNP notification will be sent only on the node where the lock request was issued. A lock will succeed only if the CsvFs filter on top of NTFS does not see any opened files.

After acquiring a lock on a CSV volume, you must close the handle used to lock that volume before opening a handle to the volume. Unlocking the volume by using FSCTL_UNLOCK_VOLUME is not sufficient.


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