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 scsi_tape(7)							scsi_tape(7)
			       Series 700 Only



 NAME
      scsi_tape - SCSI sequential access (tape) device driver

 DESCRIPTION
      SCSI sequential-access (tape) devices store a sequence of data blocks.
      Data can be read and written using either fixed or variable sized
      block mode.  If supported by the device, variable sized block mode is
      normally used (even when all blocks are the same size).  Fixed sized
      block mode is generally only used for tape devices which do not
      support variable sized blocks.  Fixed sized block mode can be used on
      some tape devices which support variable sized blocks to increase I/O
      performance.

      Generally SCSI tape devices are controlled through the mt(7) generic
      tape device interface.  This section describes features that are
      specific to SCSI tape devices.

      The SIOC_CAPACITY ioctl (see scsi(7)) can be used to determine
      remaining tape capacity for some tape devices.  The blksz field
      indicates the ``natural'' block size of the device.  This value may or
      may not be the current block size of the device.	The number of
      blocks, indicated by the lba field, is an estimate of how much data
      can be written on the remaining media.  A zero size is returned for
      devices that do not provide remaining-capacity information.  The
      quantity of data that can actually be written may be higher or lower
      than indicated, depending on such factors as block size, media
      defects, data compression, and ability to maintain streaming.

      To improve performance, most SCSI tape devices have caches.  Read-
      cache use, called "read ahead", causes the tape drive to read data in
      anticipation of read requests.  Read ahead is only apparent to users
      in the increased performance that it produces.  Write-cache use is
      called "immediate reporting".  Immediate reporting increases I/O
      performance by reporting a completed write status before the data
      being written is actually committed to media.  This allows the
      application program to supply additional data so that continuous media
      motion, called "streaming", can be achieved.  The SIOC_GET_IR ioctl
      can be used to determine if immediate-reporting functionality is
      currently being used by the device.  The value ``1'' indicates
      immediate reporting is enabled.  By default, the device driver
      attempts to enable immediate reporting.  The SIOC_SET_IR ioctl can be
      used to explicitly enable or disable immediate reporting.	 A zero
      value disables immediate reporting.  The value ``1'' enables immediate
      reporting.  The MTIOCTOP ioctl MTNOP command can be used to cause any
      cached data to be written (committed) to media.  Note that the device
      immediate reporting mode set by the SIOC_SET_IR ioctl survives between
      close() and open() calls, but not through system reboot.

      The SIOC_GET_BLOCK_SIZE ioctl indicates the device's current block
      size.  A block size of zero indicates the device is in variable-
      sized-block mode.	 A non-zero block size indicates the device is in



 Hewlett-Packard Company	    - 1 -   HP-UX Release 11i: November 2000






 scsi_tape(7)							scsi_tape(7)
			       Series 700 Only



      fixed-sized-block mode.

      The SIOC_SET_BLOCK_SIZE ioctl changes the current block size to the
      specified number of bytes.  Setting the block size to zero specifies
      that variable-sized-block mode should be used.  Any non-zero block
      size specifies that fixed-sized-block mode should be used.  By
      default, the device driver attempts to set the block size to zero
      during open.  If variable-sized-block mode is not supported by the
      device, the driver selects an appropriate block size for fixed-sized-
      block mode use.  Note that the device block size set by the
      SIOC_SET_BLOCK_SIZE ioctl survives between close() and open() calls,
      but not through system reboot.

      The SIOC_GET_BLOCK_LIMITS ioctl indicates the device's maximum and
      minimum fixed block-size limits.	The device's minimum fixed block
      size is indicated by the min_blk_size field.  The max_blk_size field
      contains the smaller of the maximum block size supported by the device
      and the maximum block size supported by the system (MAXPHYS).  This is
      the largest valid block size for the specific combination of device,
      driver, and host system being used.

      The SIOC_GET_POSITION ioctl can be used to determine the current media
      position for some devices.  For devices that support this capability,
      the resultant value can be used to reposition the media to the same
      position in the future.

      The SIOC_SET_POSITION ioctl can be used to cause media repositioning
      on some devices.	For devices that support this capability, media
      repositioning via this mechanism can generally be completed more
      quickly than might be similarly accomplished using record, filemark,
      or setmark spacing.  The argument value specified should be the result
      of a previous SIOC_GET_POSITION for that media volume.

      The following is included from <sys/scsi.h>:

	   /* ioctl support for SCSI tape commands */
	   #define SIOC_GET_IR		   _IOR('S', 14, int)
	   #define SIOC_SET_IR		   _IOW('S', 15, int)
	   #define SIOC_GET_BLOCK_SIZE	   _IOR('S', 30, int)
	   #define SIOC_SET_BLOCK_SIZE	   _IOW('S', 31, int)
	   #define SIOC_GET_BLOCK_LIMITS   _IOW('S', 32, struct scsi_block_limits)
	   #define SIOC_GET_POSITION	   _IOR('S', 33, int)
	   #define SIOC_SET_POSITION	   _IOW('S', 34, int)

	   /* structure for SIOC_GET_BLOCK_LIMITS ioctl */
	   struct scsi_block_limits {
		   unsigned min_blk_size;
		   unsigned max_blk_size;
	   };





 Hewlett-Packard Company	    - 2 -   HP-UX Release 11i: November 2000






 scsi_tape(7)							scsi_tape(7)
			       Series 700 Only



 WARNINGS
      SCSI bus and device resets cause some devices to reposition media to
      beginning-of-tape (BOT).	This unintentional media repositioning can
      cause loss of data.  The scsi_tape driver causes the first subsequent
      open() attempt to fail as an indication of potential data loss.

      The scsi_tape driver does not write filemarks at close if the media
      has been programatically repositioned.  Applications that reposition
      the media prior to closing the device should write any required
      tapemarks.

 SEE ALSO
      scsi(7), mt(7), mknod(1M).









































 Hewlett-Packard Company	    - 3 -   HP-UX Release 11i: November 2000