Returns the sector offset to the first logical cluster number (LCN) of the file system relative to the start of the volume.

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

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


hDevice [in]

A handle to the volume for which the pointer base is to be retrieved. To obtain a device handle, call the CreateFile function.

This handle must be opened with the SE_MANAGE_VOLUME_NAME access right. For more information, see File Security and Access Rights.

dwIoControlCode [in]

A control code for the operation. Use FSCTL_GET_RETRIEVAL_POINTER_BASE for this operation.


Not used with this operation; set to NULL.

nInBufferSize [in]

Not used with this operation; set to zero.

lpOutBuffer [out]

A pointer to a RETRIEVAL_POINTER_BASE structure, which receives the the sector offset to the first LCN of the file system relative to the start of the volume.

nOutBufferSize [in]

The size of the output buffer, in bytes.

lpBytesReturned [out]

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

If the output buffer is too small, the call fails, the GetLastError function returns ERROR_INSUFFICIENT_BUFFER, and lpBytesReturned is zero.

If the lpOverlapped parameter is NULL, lpBytesReturned cannot be NULL. Even when an operation returns no output data and the lpOutBuffer parameter is NULL, the DeviceIoControl function 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 the GetOverlappedResult function. If the hDevice parameter is associated with an I/O completion port, you can retrieve the number of bytes returned by calling GetQueuedCompletionStatus.

lpOverlapped [in]

A pointer to an OVERLAPPED structure.

If the hDevice parameter 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.

Return codeDescription

One or more of the following:

  • The handle used is not a valid volume handle.
  • Another parameter is not valid.

The size of the output buffer is smaller than sizeof(RETRIEVAL_POINTER_BASE).


The volume has a supported file system but the file system is not mounted. This error will not occur on NTFS.


The volume is dismounted.


The buffer passed in lpOutBuffer was not within a valid address range.


The user does not have the SE_MANAGE_VOLUME access right.


The operation was successful, and lpOutBuffer contains the sector offset to the first LCN of the file system relative to the start of the volume.



Adding the value retrieved by FSCTL_GET_RETRIEVAL_POINTER_BASE to the value retrieved by the FSCTL_GET_RETRIEVAL_POINTERS control code results in a volume-relative file extent offset.

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)




Minimum supported client

Windows 7 [desktop apps only]

Minimum supported server

Windows Server 2008 R2 [desktop apps only]


WinIoCtl.h (include Windows.h)

See also

Clusters and Extents
Disk Management Control Codes