#ifndef _NTIOAPI_H

typedef struct _FILE_FS_FULL_SIZE_INFORMATION
{
    LARGE_INTEGER TotalAllocationUnits;
    LARGE_INTEGER CallerAvailableAllocationUnits;
    LARGE_INTEGER ActualAvailableAllocationUnits;
    ULONG SectorsPerAllocationUnit;
    ULONG BytesPerSector;
} FILE_FS_FULL_SIZE_INFORMATION, *PFILE_FS_FULL_SIZE_INFORMATION;

#endif
View code on GitHub

// ntddk.h

typedef struct _FILE_FS_FULL_SIZE_INFORMATION {
  LARGE_INTEGER TotalAllocationUnits;
  LARGE_INTEGER CallerAvailableAllocationUnits;
  LARGE_INTEGER ActualAvailableAllocationUnits;
  ULONG         SectorsPerAllocationUnit;
  ULONG         BytesPerSector;
} FILE_FS_FULL_SIZE_INFORMATION, *PFILE_FS_FULL_SIZE_INFORMATION;
View the official Windows Driver Kit DDI reference

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This structure is documented in Windows Driver Kit.

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Windows Driver Kit DDI reference (ns-ntddk-_file_fs_full_size_information)

_FILE_FS_FULL_SIZE_INFORMATION structure

Description

The FILE_FS_FULL_SIZE_INFORMATION structure is used to query sector size information for a file system volume.

Members

`TotalAllocationUnits`

Total number of allocation units on the volume that are available to the user associated with the calling thread.

Microsoft Windows 2000 and later: If per-user quotas are in use, this value may be less than the total number of allocation units on the disk.

`CallerAvailableAllocationUnits`

Total number of free allocation units on the volume that are available to the user associated with the calling thread.

Windows 2000 and later: If per-user quotas are in use, this value may be less than the total number of free allocation units on the disk.

`ActualAvailableAllocationUnits`

Total number of free allocation units on the volume.

`SectorsPerAllocationUnit`

Number of sectors in each allocation unit.

`BytesPerSector`

Number of bytes in each sector.

Remarks

This information can be queried in either of the following ways:

Call FltQueryVolumeInformation or ZwQueryVolumeInformationFile, passing FileFsFullSizeInformation as the value of FileInformationClass and passing a caller-allocated, FILE_FS_FULL_SIZE_INFORMATION-structured buffer as the value of FileInformation.
Create an IRP with major function code IRP_MJ_QUERY_VOLUME_INFORMATION.

No specific access rights are required to query this information. Thus this information is available as long as the volume is accessed through an open handle to the volume itself, or to a file or directory on the volume.

The size of the buffer passed in the FileInformation parameter to FltQueryVolumeInformation or ZwQueryVolumeInformationFile must be at least sizeof (FILE_FS_FULL_SIZE_INFORMATION).

This structure must be aligned on a LONGLONG (8-byte) boundary.

FILE_FS_FULL_SIZE_INFORMATION - NtDoc