dwIoControlCode 
Specifies the control code for the operation. This value identifies the _
  specific operation to be performed and the type of device on which the _
  operation is to be performed. The following values are defined: Value Meaning 
FSCTL_ALLOW_EXTENDED_DASD_IO Signals the file system driver not to perform any _
I/O boundary checks on partition read or write calls. Instead, boundary checks _
are performed by the device driver.  
FSCTL_DELETE_REPARSE_POINT Deletes a reparse point for a file or directory. 
FSCTL_DISMOUNT_VOLUME Dismounts a volume. 
FSCTL_ENABLE_UPGRADE  Enables or disables upgrading an NTFS volume to NTFS _
  version 5. 
FSCTL_GET_COMPRESSION Obtains the compression state of a file or directory 
FSCTL_GET_HFS_INFORMATION Returns Macintosh Finder information about the file _
  associated with the input handle.  
FSCTL_GET_REPARSE_POINT Returns reparse point data for a file or directory. 
FSCTL_LOCK_VOLUME Locks a volume. 
FSCTL_QUERY_ALLOCATED_RANGES Scans a file for ranges of the file for which disk _
  space is allocated. 
FSCTL_QUERY_FAT_BPB Returns the first 36 bytes of a FAT16 or FAT12 volume. 
FSCTL_READ_COMPRESSION Reserved for future use. 
FSCTL_SET_COMPRESSION Sets the compression state of a file or directory. 
FSCTL_SET_REPARSE_POINT Sets a reparse point on a file or directory. 
FSCTL_SET_SPARSE Marks a file as a sparse file. 
FSCTL_SET_ZERO_DATA Sets a range of a files bytes to zeroes. 
FSCTL_UNLOCK_VOLUME Unlocks a volume. 
FSCTL_WRITE_COMPRESSION Reserved for future use. 
IOCTL_DISK_CHECK_VERIFY Obsolete. Use IOCTL_STORAGE_CHECK_VERIFY 
IOCTL_DISK_EJECT_MEDIA Obsolete. Use IOCTL_STORAGE_EJECT_MEDIA 
IOCTL_DISK_FORMAT_TRACKS Formats a contiguous set of disk tracks. 
IOCTL_DISK_GET_DRIVE_GEOMETRY Obtains information on the physical disk's 
' geometry. 
IOCTL_DISK_GET_DRIVE_LAYOUT Provides information about each partition on a disk. 
IOCTL_DISK_GET_MEDIA_TYPES Obsolete. Use IOCTL_STORAGE_GET_MEDIA_TYPES 
IOCTL_DISK_GET_PARTITION_INFO Obtains disk partition information. 
IOCTL_DISK_LOAD_MEDIA Obsolete. Use IOCTL_STORAGE_LOAD_MEDIA 
IOCTL_DISK_MEDIA_REMOVAL Obsolete. Use IOCTL_STORAGE_MEDIA_REMOVAL 
IOCTL_DISK_PERFORMANCE Provides disk performance information. 
IOCTL_DISK_REASSIGN_BLOCKS Maps disk blocks to spare-block pool. 
IOCTL_DISK_SET_DRIVE_LAYOUT Partitions a disk. 
IOCTL_DISK_SET_PARTITION_INFO Sets the disk partition type. 
IOCTL_DISK_VERIFY Performs logical format of a disk extent. 
IOCTL_SERIAL_LSRMST_INSERT Enables or disables placement of a line and modem _
  status data into the data stream. 
IOCTL_STORAGE_CHECK_VERIFY Checks for change in a removable-media device. 
IOCTL_STORAGE_EJECT_MEDIA Ejects media from a SCSI device. 
IOCTL_STORAGE_GET_MEDIA_TYPES Obtains information about media support. 
IOCTL_STORAGE_LOAD_MEDIA Loads media into a device. 
IOCTL_STORAGE_MEDIA_REMOVAL Enables or disables the media eject mechanism. 
 
 
For more detailed information on each control code, see its topic. In _
  particular, each topic provides details on the usage of the lpInBuffer, _
  nInBufferSize, lpOutBuffer, nOutBufferSize, and lpBytesReturned parameters.