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intro(7)							      intro(7)

       intro - introduction to device special files

       This  section  describes	 the  device special files (DSFs) and hardware
       paths used to access HP peripherals and device drivers.	The  names  of
       the  entries  are  generally  derived  from  the	 type  of device being
       described (disk, tape, terminal, and so on.),  not  the	names  of  the
       device  special files or device drivers themselves.  Characteristics of
       both the hardware device and the corresponding HP-UX device driver  are
       discussed where applicable.

   Device Types
       Devices	can  be	 classified  in	 two device access modes, and A raw or
       character-mode device, such as a line printer,  transfers  data	in  an
       unbuffered stream and uses a character device special file.

       A  block-mode  device, as the name implies, transfers data in blocks by
       means of the system's normal buffering mechanism.   Block  devices  use
       block  device  special  files and may have a character device interface

   Device File Naming Convention
       A device special file name becomes associated with a  device  when  the
       file  is	 created,  either  automatically by the special file daemon or
       explicitly with the or command.	When creating device special files, it
       is recommended that the following standard naming convention be used:

	      subdir	An  optional  subdirectory  for	 the device class (for
			example, for raw device special files for  disks,  for
			block  device  special	files  for disks, for raw tape

	      class	The class of device, such as or

	      #		The instance number assigned by the  operating	system
			to  the	 device.  Each class of device has its own set
			of instance numbers, so each combination of class  and
			instance number refers to exactly one device.

	      options	Further	 qualifiers,  such as disk partition tape den‐
			sity selection for a tape device, or surface  specifi‐
			cation for magneto-optical media.

       Naming  conventions  for	 each  type  of	 device are described in their
       respective manpage entries.

       Legacy mass storage device special files have a different  naming  con‐
       vention	that  encodes the hardware path; this is described in the sec‐

   Cluster Device Special Files
       A cluster device special file provides a consistent set of device  spe‐
       cial  files  across a set of cluster nodes.  The cluster device special
       files of a LUN will be the same on any node in a specified set of nodes
       that share the LUN.

       The set of cluster nodes across which cluster device special files need
       to be created can be specified using the cmsetdsfgroup(1M) command.

       The  cluster  device  special  files  can  be   displayed   using   the
       io_cdsf_config(1M) command.

       Cluster	device special files are created in both block access mode and
       raw (character) access mode.  Block mode cluster device	special	 files
       are created in the directory, and character mode cluster device special
       files are created in the directory.

       Cluster device special file creation requires that Serviceguard A.11.20
       be  installed  and  patched  with  the cluster-wide device special file
       (cDSF) enhancement, and possibly other dependent patches.  See the lat‐
       est version of the for more information.

   Hardware Paths
       Hardware path information, as well as class names and instance numbers,
       can be derived from output; see ioscan(1M).  There are three  different
       types  of paths to a device: and All three are numeric strings of hard‐
       ware components, notated sequentially from the system  bus  address  to
       the device address.  Each number typically represents the location of a
       hardware component on the path to the device.

       The is composed of a series of bus-nexus addresses separated  by	 slash
       characters,  leading  to	 a  host  bus adapter (HBA).  Beneath the HBA,
       additional address elements are separated by  period  characters.   All
       the elements are represented in decimal.	 This is the format printed by
       default by the command for most devices.	 An example of a legacy	 hard‐
       ware path is

       The  is	used  for  mass	 storage  devices, also known as logical units
       (LUNs).	It is identical in format to a legacy hardware path, up to the
       HBA.   Beneath the HBA, additional elements are printed in hexadecimal.
       The leading elements representing a transport-dependent target address,
       and  the	 final element is a LUN address, which is a 64-bit representa‐
       tion of the LUN identifier reported by  the  target.   This  format  is
       printed	by the command when the option is specified.  The string is an
       example of a lunpath hardware path.

       Note that the address elements beneath the HBA may  not	correspond  to
       physical	 hardware addresses; instead, the lunpath hardware path should
       be considered a handle, not a physical path to the device.

       The is a virtualized path that can represent multiple hardware paths to
       a  single  mass	storage	 device.   Instead  of	a  series of bus-nexus
       addresses leading to the HBA, there is a virtual	 bus-nexus  (known  as
       the  with  an  address  of 64000.  Addressing beneath that virtual root
       node consists of a virtual bus address and a  virtual  LUN  identifier,
       delimited by slash characters.  The string is an example of a LUN hard‐
       ware path.

       As a virtualized path, the LUN hardware path is only a  handle  to  the
       LUN,  and does not represent the LUN's physical location; rather, it is
       linked to the LUN's World Wide Identifier (WWID).  Thus, it remains the
       same  if new physical paths to the device are added, if existing physi‐
       cal paths are removed, or if any of the physical paths  changes.	  This
       LUN  binding  persists across reboots, but it is not guaranteed to per‐
       sist  across  installations  —  that  is,  reinstalling	a  system   or
       installing  an identically configured system may create a different set
       of LUN hardware paths.

   Device File Types (Mass Storage Devices)
       Mass storage devices, such as disk devices and tape devices,  have  two
       types  of  device files, device special files and device special files.
       Both can be used to access the mass storage device  independently,  and
       can coexist on the same system.

       A  device special file is associated with a LUN hardware path, and thus
       transparently supports agile addressing	and  multipathing.   In	 other
       words,  a  persistent  device  special  file is unchanged if the LUN is
       moved from one HBA to  another,	moved  from  one  switch/hub  port  to
       another,	 presented via a different target port to the host, or config‐
       ured with multiple hardware paths.  Like the  LUN  hardware  path,  the
       binding	of  device special file to device persists across reboots, but
       is not guaranteed to persist across installations.  The device  special
       file  name  follows the standard naming convention above, and the minor
       number contains no hardware path information.

       A device special file is locked to a particular physical hardware path,
       and does not support agile addressing.  Such a device special file con‐
       tains hardware path information such as SCSI bus, target,  and  LUN  in
       the  device  file  name	and minor number.  Specifically, the class and
       instance portions of the device special	file  name  indicate  hardware
       path information and are in the format as follows:

	      The  instance  number  assigned  by  the operating system to the
	      interface card,
			in decimal.  It is a decimal number with a range of  0
			to  255.   There  is  no  direct  correlation  between
			instance number and physical slot number.

	      The target address on a remote bus (for example, SCSI address).
			It is a decimal number with a typical range  of	 0  to

	      The device unit number at the target address
			(for example, the LUN in a SCSI device).  It is a dec‐
			imal number with a typical range of 0 to 7.

       Note that the legacy naming convention supports a maximum of 256 exter‐
       nal  buses  and	a  maximum  of	32768 LUNs.  Systems with mass storage
       devices beyond those limits will be unable to address them using legacy
       naming conventions.

       Legacy  device  special files are deprecated, and their support will be
       removed in a future release of HP-UX.

   Viewing Mass Storage
       With the advent of persistent and legacy device special files, commands
       dealing	with mass storage can choose between two of the I/O system.  A
       command presenting the view uses legacy device special files and legacy
       hardware paths.	The view uses persistent device special files, lunpath
       hardware paths, and LUN hardware paths.

       Depending on the command, both views may be presented, or the choice of
       view  may be controlled by a command option or an environment variable.
       For example, the command shows the legacy view by default, and switches
       to the agile view if the option is specified.

   Example 1
       The following is an example of a persistent device special file name:

       where  indicates	 block	disk  access  and  indicates  device class and
       instance number 3.  The absence of indicates access to the entire disk;
       see disk(7) for details.

   Example 2
       The following is an example of a legacy disk device special file name:

       where  indicates block disk access and indicates logical disk access at
       interface card instance 0, target address 6, and unit 0.	 The indicates
       access to section 2 of the disk.

   Example 3
       The  following  is  an example of a persistent tape device special file

       where indicates raw magnetic tape, indicates tape device instance  num‐
       ber 4, and identifies the tape format as QIC150; see mt(7) for details.

   Example 4
       The following is an example of a cluster device special file name:

       where  indicates	 block	cluster disk access and indicates device class
       disk and instance number 5.

       The support of legacy device special files is deprecated	 and  will  be
       removed in a future release of HP-UX.

       cmsetdsfgroup(1M),  insf(1M),  io_cdsf_config(1M) ioscan(1M), lssf(1M),
       mksf(1M), mknod(1M), hier(5), introduction(9).

       Manuals on the technical documentation website,


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