disk man page on HP-UX

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disk(7)								       disk(7)

       disk - direct disk access

       This  entry  describes the actions of HP-UX disk drivers when referring
       to a disk as either a block-special or character-special (raw) device.

   Device File Naming Conventions
       Standard disk device files are named according to the following conven‐
       tions (see intro(7)):

	      Block-mode Devices

	      Character-mode Devices

	      Legacy block-mode Devices

	      Legacy character-mode Devices

       Legacy  device  special filenames are those used on HP-UX 11i Version 2
       and earlier releases.  They can still be used for backward  compatibil‐
       ity,  but only for part of the configuration within the limits of HP-UX
       11i Version 2.

       The component parts of the device filename are constructed as follows:

	      N	   Required. A decimal number corresponding  to	 the  instance
		   number  assigned to the direct access device by the operat‐
		   ing system.

	      X	   Required if is specified. A decimal number corresponding to
		   a partition number.

		   Identifies	the   following	  hexadecimal  digits  as  the
		   "Instance" of the interface card.

	      x	   Hexadecimal number identifying controlling  bus  interface,
		   also	 known	as  the "Instance" of this interface card. The
		   instance value is displayed in the ioscan(1M) output,  col‐
		   umn "I" for the H/W Type, "INTERFACE".

	      Identifies the following hexadecimal digits as a "drive number"
		   or "target".

	      y	   Hexadecimal	number	identifying the drive or target number
		   (bus address).

	      Identifies the following hexadecimal digits as a "unit number".

	      n	   Hexadecimal unit number within the device.

	      Optional.	 Defaults to that corresponding to whole disk.
		   Identifies the following value as a "section number".

	      m	   Required if is specified.  Defaults to  section  0  (zero),
		   whole disk.	Drive section number.

       Assignment  of  controller,  drive, logical unit and section numbers is
       described in the system administrator manuals for your system.

   Block-special access
       Block-special device files access disks via the system's	 block	buffer
       cache  mechanism.   Buffering  is  done	in  such a way that concurrent
       access through multiple opens and mounting the same physical device  is
       correctly handled to avoid operation sequencing errors.	The block buf‐
       fer cache permits the system to do physical I/O operations when	conve‐
       nient.	This  means  that physical write operations may occur substan‐
       tially later in time than their corresponding logical  write  requests.
       This  also  means that physical read operations may occur substantially
       earlier in time than their corresponding logical read requests.

       Block-special files can be read and written without regard to  physical
       disk  records.	Block-special  file  and  calls	 requiring disk access
       result in one or more byte (typically 2048 byte) transfers between  the
       disk  and the block buffer cache.  Applications using the block-special
       device should ensure that they do not read or write  past  the  end  of
       last  sized  block  in  the  device  file.   Because  the  interface is
       buffered, accesses past this point behave unpredictably.

   Character-special access
       Character-special device files access disks without buffering and  sup‐
       port  the  direct  transmission of data between the disk and the user's
       read or write buffer.  Disk access through the character	 special  file
       interface  causes  all  physical	 I/O operations to be completed before
       control returns from the call.  A single read or write operation up  to
       bytes  (typically  64 Kbytes or 256 Kbytes) results in exactly one disk
       operation.  Requests larger than this are broken	 up  automatically  by
       the operating system.  Since large I/O operations via character-special
       files avoid block buffer cache handling and result in fewer disk opera‐
       tions,  they  are  typically  more efficient than similar block-special
       file operations.

       There may be implementation-dependent restrictions on the alignment  of
       the  user buffer in memory for character special file and calls.	 Also,
       each read and write operation must begin and end	 on  a	logical	 block
       boundary	 and  must  be	a whole number of logical blocks in size.  The
       logical block size is a hardware-dependent value that  can  be  queried
       with the and ioctl calls, which are described below.

       In  addition  to	 reading  and writing data, the character-special file
       interface can be used to obtain device specific information and to per‐
       form  special  operations.  These operations are controlled through use
       of ioctl calls.	Details related to these ioctls are contained in

       The and ioctl can be used  to  obtain  device  specific	identification
       information.   The information returned includes the disk's model iden‐
       tification, the disk interface type,  maximum  offset  address,	device
       type, and the disk's logical block size.

       The ioctl can be used to obtain the capacity of a disk device in units.
       is defined in

       The ioctl can be used to obtain and release exclusive access to a  disk
       device.	Exclusive access is required for some special operations, such
       as media reformatting, and may be  desirable  in	 other	circumstances.
       The  value one specifies that exclusive access is requested.  The value
       zero specifies the exclusive  access  should  be	 released.   Exclusive
       access  causes  other open requests to fail.  Exclusive access can only
       be granted when the device is not currently opened  in  block-mode  and
       there  is  only one open file table entry for that disk device (the one
       accessible to the exclusive access requester).

       WARNING:	 The  ioctl  does  NOT	prevent	 the  use  of  pass-thru  (see
       scsi_ctl(7)) device files, after the ioctl is issued.

       The following errors can be returned by a disk device driver call:

	      Required permission is denied for the the device or operation.

	      I/O	     error (e.g., media defect or device communication

	      From an	     call: the device is not a disk device.  For other
			     calls:  Invalid  request or parameter.  Note that
			     for legacy, 32-bit access, this error can	result
			     when  the	size of the device overflows the argu‐
			     ment of the or ioctls.

	      If resulting from an
			     call, this indicates there is no  device  at  the
			     specified	address.   For other calls, this indi‐
			     cates the specified address is out	 of  range  or
			     the device can no longer be accessed.

       The  interaction	 of block-special and character-special file access to
       the same -sized block is	 not  specified,  and  in  general  is	unpre‐

       On  some systems, having both a mounted file system and a block special
       file open on the same device  can  cause	 unpredictable	results;  this
       should  be avoided if possible.	This is because it may be possible for
       some files to have private buffers in some systems.

       Although disk devices have historically had small (typically  512-byte)
       block  sizes, some disk devices (such as optical disks and disk arrays)
       have relatively large block sizes.  Applications using direct raw  disk
       access  should  use  calls to determine appropriate I/O operation sizes
       and alignments.

       Any disk with removable media (for example, floppy or CD-ROM)  contain‐
       ing  a  mounted	file  system  should  not  be  removed	prior to being
       unmounted.  Removal of disk media containing mounted  file  systems  is
       likely to result in file system errors and system panics.

       was developed by HP and AT&T.

       ioscan(1M), mknod(1M), scsi_ctl(7), intro(7).

       System Administrator manuals included with your system.


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