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ST(4)			   Linux Programmer's Manual			 ST(4)

       st - SCSI tape device

       #include <sys/mtio.h>

       int ioctl(int fd, int request [, (void *)arg3]);
       int ioctl(int fd, MTIOCTOP, (struct mtop *)mt_cmd);
       int ioctl(int fd, MTIOCGET, (struct mtget *)mt_status);
       int ioctl(int fd, MTIOCPOS, (struct mtpos *)mt_pos);

       The st driver provides the interface to a variety of SCSI tape devices.
       Currently, the driver takes control of all  detected  devices  of  type
       "sequential-access".  The st driver uses major device number 9.

       Each  device  uses eight minor device numbers.  The lowermost five bits
       in the minor numbers are assigned sequentially in the order  of	detec-
       tion.   In  the 2.6 kernel, the bits above the eight lowermost bits are
       concatenated to the five lowermost bits to form the tape	 number.   The
       minor numbers can be grouped into two sets of four numbers: the princi-
       pal (auto-rewind) minor device numbers, n, and the  "no-rewind"	device
       numbers,	 (n  + 128).  Devices opened using the principal device number
       will be sent a REWIND command when they	are  closed.   Devices	opened
       using  the  "no-rewind"	device	number	will not.  (Note that using an
       auto-rewind device for positioning the tape with, for instance, mt does
       not  lead  to the desired result: the tape is rewound after the mt com-
       mand and the next command starts from the beginning of the tape).

       Within each group, four minor numbers are available to  define  devices
       with different characteristics (block size, compression, density, etc.)
       When the system starts up, only the first  device  is  available.   The
       other  three are activated when the default characteristics are defined
       (see below).  (By changing compile-time constants, it  is  possible  to
       change  the  balance  between the maximum number of tape drives and the
       number of minor numbers for each drive.	The default allocation	allows
       control	of 32 tape drives.  For instance, it is possible to control up
       to 64 tape drives with two minor numbers for different options.)

       Devices are typically created by:

	   mknod -m 666 /dev/st0 c 9 0
	   mknod -m 666 /dev/st0l c 9 32
	   mknod -m 666 /dev/st0m c 9 64
	   mknod -m 666 /dev/st0a c 9 96
	   mknod -m 666 /dev/nst0 c 9 128
	   mknod -m 666 /dev/nst0l c 9 160
	   mknod -m 666 /dev/nst0m c 9 192
	   mknod -m 666 /dev/nst0a c 9 224

       There is no corresponding block device.

       The driver uses an internal buffer that has to be large enough to  hold
       at  least  one  tape  block.   In kernels before 2.1.121, the buffer is
       allocated as one contiguous block.  This limits the block size  to  the
       largest	contiguous  block  of memory the kernel allocator can provide.
       The limit is currently 128 kB for 32-bit architectures and 256  kB  for
       64-bit architectures.  In newer kernels the driver allocates the buffer
       in several parts if necessary.  By default, the maximum number of parts
       is  16.	 This means that the maximum block size is very large (2 MB if
       allocation of 16 blocks of 128 kB succeeds).

       The driver's internal buffer size is determined by a compile-time  con-
       stant  which  can be overridden with a kernel startup option.  In addi-
       tion to this, the driver tries to allocate a larger temporary buffer at
       run  time if necessary.	However, run-time allocation of large contigu-
       ous blocks of memory may fail and it is advisable not to rely too  much
       on  dynamic  buffer  allocation	with  kernels older than 2.1.121 (this
       applies also to demand-loading the driver with kerneld or kmod).

       The driver does not specifically support any tape drive brand or model.
       After  system start-up the tape device options are defined by the drive
       firmware.  For example, if the drive firmware selects fixed-block mode,
       the tape device uses fixed-block mode.  The options can be changed with
       explicit ioctl(2) calls and remain in effect when the device is	closed
       and reopened.  Setting the options affects both the auto-rewind and the
       nonrewind device.

       Different options can be specified for the different devices within the
       subgroup	 of  four.  The options take effect when the device is opened.
       For example, the system administrator can define one device that writes
       in  fixed-block mode with a certain block size, and one which writes in
       variable-block mode (if the drive supports both modes).

       The driver supports tape partitions if they are supported by the drive.
       (Note that the tape partitions have nothing to do with disk partitions.
       A partitioned tape can be seen as  several  logical  tapes  within  one
       medium.)	  Partition  support  has to be enabled with an ioctl(2).  The
       tape location is	 preserved  within  each  partition  across  partition
       changes.	 The partition used for subsequent tape operations is selected
       with an ioctl(2).  The partition switch is executed together  with  the
       next  tape  operation in order to avoid unnecessary tape movement.  The
       maximum number of partitions on a tape is  defined  by  a  compile-time
       constant	 (originally  four).  The driver contains an ioctl(2) that can
       format a tape with either one or two partitions.

       Device /dev/tape is usually created as a	 hard  or  soft	 link  to  the
       default tape device on the system.

       Starting	 from  kernel 2.6.2, the driver exports in the sysfs directory
       /sys/class/scsi_tape the attached devices and some parameters  assigned
       to the devices.

   Data transfer
       The  driver  supports  operation in both fixed-block mode and variable-
       block mode (if supported by the drive).	In fixed-block mode the	 drive
       writes blocks of the specified size and the block size is not dependent
       on the byte counts of the write system calls.  In  variable-block  mode
       one tape block is written for each write call and the byte count deter-
       mines the size of the corresponding tape block.	Note that  the	blocks
       on  the tape don't contain any information about the writing mode: when
       reading, the only important thing is to use commands  that  accept  the
       block sizes on the tape.

       In  variable-block  mode the read byte count does not have to match the
       tape block size exactly.	 If the byte count is  larger  than  the  next
       block on tape, the driver returns the data and the function returns the
       actual block size.  If the block size is larger than the byte count, an
       error is returned.

       In  fixed-block mode the read byte counts can be arbitrary if buffering
       is enabled, or a multiple of the tape block size if buffering  is  dis-
       abled.	Kernels	 before 2.1.121 allow writes with arbitrary byte count
       if buffering is enabled.	 In all other  cases  (kernel  before  2.1.121
       with buffering disabled or newer kernel) the write byte count must be a
       multiple of the tape block size.

       In the 2.6 kernel, the driver tries to use direct transfers between the
       user  buffer  and  the  device.	 If this is not possible, the driver's
       internal buffer is used.	 The reasons for not  using  direct  transfers
       include improper alignment of the user buffer (default is 512 bytes but
       this can be changed by the HBA driver), one or more pages of  the  user
       buffer not reachable by the SCSI adapter, and so on.

       A  filemark is automatically written to tape if the last tape operation
       before close was a write.

       When a filemark is encountered while reading,  the  following  happens.
       If  there  are data remaining in the buffer when the filemark is found,
       the buffered data is returned.  The next read returns zero bytes.   The
       following  read	returns	 data from the next file.  The end of recorded
       data is signaled by returning  zero  bytes  for	two  consecutive  read
       calls.  The third read returns an error.

       The  driver  supports three ioctl(2) requests.  Requests not recognized
       by the st driver are passed to the SCSI driver.	The definitions	 below
       are from /usr/include/linux/mtio.h:

   MTIOCTOP -- perform a tape operation
       This request takes an argument of type (struct mtop *).	Not all drives
       support all operations.	The driver returns an EIO error if  the	 drive
       rejects an operation.

	   /* Structure for MTIOCTOP - mag tape op command: */
	   struct mtop {
	       short   mt_op;	    /* operations defined below */
	       int     mt_count;    /* how many of them */

       Magnetic Tape operations for normal tape use:

       MTBSF	     Backward space over mt_count filemarks.

       MTBSFM	     Backward  space  over mt_count filemarks.	Reposition the
		     tape to the EOT side of the last filemark.

       MTBSR	     Backward space over mt_count records (tape blocks).

       MTBSS	     Backward space over mt_count setmarks.

       MTCOMPRESSION Enable compression of  tape  data	within	the  drive  if
		     mt_count  is  nonzero and disable compression if mt_count
		     is zero.  This command uses the MODE page 15 supported by
		     most DATs.

       MTEOM	     Go	 to  the  end  of  the	recorded  media (for appending

       MTERASE	     Erase tape.  With 2.6  kernel,  short  erase  (mark  tape
		     empty)  is performed if the argument is zero.  Otherwise,
		     long erase (erase all) is done.

       MTFSF	     Forward space over mt_count filemarks.

       MTFSFM	     Forward space over mt_count  filemarks.   Reposition  the
		     tape to the BOT side of the last filemark.

       MTFSR	     Forward space over mt_count records (tape blocks).

       MTFSS	     Forward space over mt_count setmarks.

       MTLOAD	     Execute  the SCSI load command.  A special case is avail-
		     able for some HP autoloaders.  If mt_count	 is  the  con-
		     stant  MT_ST_HPLOADER_OFFSET plus a number, the number is
		     sent to the drive to control the autoloader.

       MTLOCK	     Lock the tape drive door.

       MTMKPART	     Format the tape into one or two partitions.  If  mt_count
		     is	 positive, it gives the size of partition 1 and parti-
		     tion 0 contains the rest of the  tape.   If  mt_count  is
		     zero,  the	 tape  is  formatted into one partition.  From
		     kernel version 4.6, a  negative  mt_count	specifies  the
		     size  of  partition  0  and the rest of the tape contains
		     partition 1.  The physical ordering of partitions depends
		     on	 the  drive.   This command is not allowed for a drive
		     unless the partition support is  enabled  for  the	 drive
		     (see MT_ST_CAN_PARTITIONS below).

       MTNOP	     No	 op--flushes  the  driver's  buffer  as a side effect.
		     Should be used before reading status with MTIOCGET.

       MTOFFL	     Rewind and put the drive off line.

       MTRESET	     Reset drive.

       MTRETEN	     Re-tension tape.

       MTREW	     Rewind.

       MTSEEK	     Seek to the tape  block  number  specified	 in  mt_count.
		     This  operation  requires either a SCSI-2 drive that sup-
		     ports the LOCATE command (device-specific address)	 or  a
		     Tandberg-compatible   SCSI-1   drive  (Tandberg,  Archive
		     Viper, Wangtek, ...).  The block  number  should  be  one
		     that  was	previously returned by MTIOCPOS if device-spe-
		     cific addresses are used.

       MTSETBLK	     Set the drive's block length to the  value	 specified  in
		     mt_count.	A block length of zero sets the drive to vari-
		     able block size mode.

       MTSETDENSITY  Set the tape density to the code in mt_count.   The  den-
		     sity  codes  supported  by	 a drive can be found from the
		     drive documentation.

       MTSETPART     The active partition is switched to mt_count.  The parti-
		     tions  are	 numbered  from	 zero.	 This  command	is not
		     allowed for a  drive  unless  the	partition  support  is
		     enabled for the drive (see MT_ST_CAN_PARTITIONS below).

       MTUNLOAD	     Execute  the  SCSI	 unload	 command  (does	 not eject the

       MTUNLOCK	     Unlock the tape drive door.

       MTWEOF	     Write mt_count filemarks.

       MTWSM	     Write mt_count setmarks.

       Magnetic Tape operations for setting of device options  (by  the	 supe-

	       Set  various drive and driver options according to bits encoded
	       in mt_count.  These consist of the drive's  buffering  mode,  a
	       set  of	Boolean	 driver	 options,  the buffer write threshold,
	       defaults for the block size and density, and timeouts (only  in
	       kernels 2.1 and later).	A single operation can affect only one
	       item in the list above (the Booleans counted as one item.)

	       A value having zeros in the high-order 4 bits will be  used  to
	       set the drive's buffering mode.	The buffering modes are:

		   0   The drive will not report GOOD status on write commands
		       until the data  blocks  are  actually  written  to  the

		   1   The  drive  may report GOOD status on write commands as
		       soon as all  the	 data  has  been  transferred  to  the
		       drive's internal buffer.

		   2   The  drive  may report GOOD status on write commands as
		       soon as (a) all the data has been  transferred  to  the
		       drive's internal buffer, and (b) all buffered data from
		       different initiators has been successfully  written  to
		       the medium.

	       To  control  the	 write	threshold  the	value in mt_count must
	       include the constant MT_ST_WRITE_THRESHOLD bitwise ORed with  a
	       block  count  in	 the  low  28 bits.  The block count refers to
	       1024-byte blocks, not the physical block size on the tape.  The
	       threshold  cannot exceed the driver's internal buffer size (see
	       DESCRIPTION, above).

	       To set and clear the Boolean options the value in mt_count must
	       include one of the constants MT_ST_BOOLEANS, MT_ST_SETBOOLEANS,
	       MT_ST_CLEARBOOLEANS, or	MT_ST_DEFBOOLEANS  bitwise  ORed  with
	       whatever	 combination  of  the  following  options  is desired.
	       Using MT_ST_BOOLEANS the options	 can  be  set  to  the	values
	       defined	in the corresponding bits.  With MT_ST_SETBOOLEANS the
	       options can  be	selectively  set  and  with  MT_ST_DEFBOOLEANS
	       selectively cleared.

	       The  default  options for a tape device are set with MT_ST_DEF-
	       BOOLEANS.  A nonactive tape device (e.g., device with minor  32
	       or  160)	 is  activated	when  the  default  options for it are
	       defined the first time.	An activated device inherits from  the
	       device activated at start-up the options not set explicitly.

	       The Boolean options are:

	       MT_ST_BUFFER_WRITES (Default: true)
		      Buffer  all  write  operations  in fixed-block mode.  If
		      this option is false and the drive uses  a  fixed	 block
		      size,  then  all write operations must be for a multiple
		      of the block size.  This option must  be	set  false  to
		      write reliable multivolume archives.

	       MT_ST_ASYNC_WRITES (Default: true)
		      When  this option is true, write operations return imme-
		      diately without waiting for the data to  be  transferred
		      to  the drive if the data fits into the driver's buffer.
		      The write threshold determines how full the buffer  must
		      be  before  a  new  SCSI	write  command is issued.  Any
		      errors reported by the drive will be held until the next
		      operation.  This option must be set false to write reli-
		      able multivolume archives.

	       MT_ST_READ_AHEAD (Default: true)
		      This option causes the driver to provide read  buffering
		      and  read-ahead  in fixed-block mode.  If this option is
		      false and the drive uses a fixed block  size,  then  all
		      read  operations	must  be  for  a multiple of the block

	       MT_ST_TWO_FM (Default: false)
		      This option modifies the driver behavior when a file  is
		      closed.	The  normal  action is to write a single file-
		      mark.  If the option is true, the driver will write  two
		      filemarks and backspace over the second one.

		      Note:  This  option  should not be set true for QIC tape
		      drives since they are unable to  overwrite  a  filemark.
		      These  drives detect the end of recorded data by testing
		      for blank tape rather than  two  consecutive  filemarks.
		      Most  other  current  drives  also  detect  the  end  of
		      recorded data and using two filemarks is usually	neces-
		      sary  only when interchanging tapes with some other sys-

	       MT_ST_DEBUGGING (Default: false)
		      This option turns on various debugging messages from the
		      driver  (effective  only if the driver was compiled with
		      DEBUG defined nonzero).

	       MT_ST_FAST_EOM (Default: false)
		      This option  causes  the	MTEOM  operation  to  be  sent
		      directly to the drive, potentially speeding up the oper-
		      ation but causing the driver to lose track of  the  cur-
		      rent  file  number  normally  returned  by  the MTIOCGET
		      request.	If MT_ST_FAST_EOM is false,  the  driver  will
		      respond  to  an  MTEOM  request  by forward spacing over

	       MT_ST_AUTO_LOCK (Default: false)
		      When this option is true, the drive door is locked  when
		      the device is opened and unlocked when it is closed.

	       MT_ST_DEF_WRITES (Default: false)
		      The  tape	 options (block size, mode, compression, etc.)
		      may change when changing from one	 device	 linked	 to  a
		      drive to another device linked to the same drive depend-
		      ing on how the devices are defined.  This option defines
		      when  the changes are enforced by the driver using SCSI-
		      commands and when the drives auto-detection capabilities
		      are  relied  upon.   If this option is false, the driver
		      sends the SCSI-commands immediately when the  device  is
		      changed.	 If  the option is true, the SCSI-commands are
		      not sent until a write is requested.  In this case,  the
		      drive  firmware  is allowed to detect the tape structure
		      when reading and the SCSI-commands are used only to make
		      sure  that  a  tape  is written according to the correct

	       MT_ST_CAN_BSR (Default: false)
		      When read-ahead is used,	the  tape  must	 sometimes  be
		      spaced  backward to the correct position when the device
		      is closed and the SCSI command to	 space	backward  over
		      records  is  used	 for  this purpose.  Some older drives
		      can't process this command reliably and this option  can
		      be  used	to instruct the driver not to use the command.
		      The end result is that, with read-ahead and  fixed-block
		      mode,  the tape may not be correctly positioned within a
		      file when the device is closed.  With  2.6  kernel,  the
		      default is true for drives supporting SCSI-3.

	       MT_ST_NO_BLKLIMS (Default: false)
		      Some drives don't accept the READ BLOCK LIMITS SCSI com-
		      mand.  If this is used, the driver does not use the com-
		      mand.   The  drawback  is	 that  the  driver can't check
		      before sending commands if the selected  block  size  is
		      acceptable to the drive.

	       MT_ST_CAN_PARTITIONS (Default: false)
		      This  option  enables  support  for  several  partitions
		      within a tape.  The option applies to all devices linked
		      to a drive.

	       MT_ST_SCSI2LOGICAL (Default: false)
		      This  option  instructs  the  driver  to use the logical
		      block addresses defined in the SCSI-2 standard when per-
		      forming  the  seek and tell operations (both with MTSEEK
		      and MTIOCPOS commands and when changing tape partition).
		      Otherwise,  the  device-specific addresses are used.  It
		      is highly advisable to set this option if the drive sup-
		      ports  the  logical  addresses  because  they count also
		      filemarks.  There are some drives that support only  the
		      logical block addresses.

	       MT_ST_SYSV (Default: false)
		      When  this  option  is enabled, the tape devices use the
		      SystemV semantics.  Otherwise,  the  BSD	semantics  are
		      used.   The most important difference between the seman-
		      tics is what happens when a device used for  reading  is
		      closed: in System V semantics the tape is spaced forward
		      past the next filemark if this has  not  happened	 while
		      using the device.	 In BSD semantics the tape position is
		      not changed.

	       MT_NO_WAIT (Default: false)
		      Enables immediate mode (i.e., don't wait for the command
		      to finish) for some commands (e.g., rewind).

	       An example:

		   struct mtop mt_cmd;
		   mt_cmd.mt_op = MTSETDRVBUFFER;
		   mt_cmd.mt_count = MT_ST_BOOLEANS |
		   ioctl(fd, MTIOCTOP, mt_cmd);

	       The   default   block  size  for	 a  device  can	 be  set  with
	       MT_ST_DEF_BLKSIZE and the default density code can be set  with
	       MT_ST_DEFDENSITY.  The values for the parameters are or'ed with
	       the operation code.

	       With kernels 2.1.x and later, the timeout  values  can  be  set
	       with  the subcommand MT_ST_SET_TIMEOUT ORed with the timeout in
	       seconds.	 The long timeout (used for rewinds and other commands
	       that may take a long time) can be set with MT_ST_SET_LONG_TIME-
	       OUT.  The kernel defaults are very long to  make	 sure  that  a
	       successful command is not timed out with any drive.  Because of
	       this, the driver may seem stuck even if it is only waiting  for
	       the  timeout.  These commands can be used to set more practical
	       values for a specific drive.  The timeouts set for  one	device
	       apply for all devices linked to the same drive.

	       Starting	 from kernels 2.4.19 and 2.5.43, the driver supports a
	       status bit which indicates whether the drive requests cleaning.
	       The  method used by the drive to return cleaning information is
	       set using the MT_ST_SEL_CLN subcommand.	If the value is	 zero,
	       the  cleaning  bit  is  always  zero.  If the value is one, the
	       TapeAlert data defined in the SCSI-3 standard is used (not  yet
	       implemented).   Values  2-17 are reserved.  If the lowest eight
	       bits are >= 18, bits from the extended  sense  data  are	 used.
	       The  bits 9-16 specify a mask to select the bits to look at and
	       the bits 17-23 specify the bit pattern to look for.  If the bit
	       pattern	is  zero, one or more bits under the mask indicate the
	       cleaning request.  If the pattern is nonzero, the pattern  must
	       match the masked sense data byte.

   MTIOCGET -- get status
       This request takes an argument of type (struct mtget *).

	   /* structure for MTIOCGET - mag tape get status command */
	   struct mtget {
	       long	mt_type;
	       long	mt_resid;
	       /* the following registers are device dependent */
	       long	mt_dsreg;
	       long	mt_gstat;
	       long	mt_erreg;
	       /* The next two fields are not always used */
	       daddr_t	mt_fileno;
	       daddr_t	mt_blkno;

       mt_type	  The  header  file  defines  many values for mt_type, but the
		  current driver reports only  the  generic  types  MT_ISSCSI1
		  (Generic SCSI-1 tape) and MT_ISSCSI2 (Generic SCSI-2 tape).

       mt_resid	  contains the current tape partition number.

       mt_dsreg	  reports  the drive's current settings for block size (in the
		  low 24 bits) and density (in the high 8 bits).  These fields
		  are	defined	 by  MT_ST_BLKSIZE_SHIFT,  MT_ST_BLKSIZE_MASK,

       mt_gstat	  reports generic  (device  independent)  status  information.
		  The  header  file  defines  macros  for testing these status

		  GMT_EOF(x): The tape is positioned  just  after  a  filemark
		      (always false after an MTSEEK operation).

		  GMT_BOT(x):  The  tape is positioned at the beginning of the
		      first file (always false after an MTSEEK operation).

		  GMT_EOT(x): A tape operation has reached the physical End Of

		  GMT_SM(x):  The  tape	 is  currently positioned at a setmark
		      (always false after an MTSEEK operation).

		  GMT_EOD(x): The tape is positioned at the  end  of  recorded

		  GMT_WR_PROT(x):  The	drive  is  write-protected.   For some
		      drives this can also mean that the drive does  not  sup-
		      port writing on the current medium type.

		  GMT_ONLINE(x):  The last open(2) found the drive with a tape
		      in place and ready for operation.

		  GMT_D_6250(x), GMT_D_1600(x), GMT_D_800(x):  This  "generic"
		      status  information  reports the current density setting
		      for 9-track 1/2" tape drives only.

		  GMT_DR_OPEN(x): The drive does not have a tape in place.

		  GMT_IM_REP_EN(x): Immediate report mode.  This bit is set if
		      there  are  no  guarantees that the data has been physi-
		      cally written to the tape when the write	call  returns.
		      It is set zero only when the driver does not buffer data
		      and the drive is set not to buffer data.

		  GMT_CLN(x): The drive has requested  cleaning.   Implemented
		      in kernels since 2.4.19 and 2.5.43.

       mt_erreg	  The  only  field  defined in mt_erreg is the recovered error
		  count in the low 16 bits (as defined by  MT_ST_SOFTERR_SHIFT
		  and  MT_ST_SOFTERR_MASK.   Due to inconsistencies in the way
		  drives report recovered errors,  this	 count	is  often  not
		  maintained (most drives do not by default report soft errors
		  but this can be changed with a SCSI MODE SELECT command).

       mt_fileno  reports the current file number (zero-based).	 This value is
		  set to -1 when the file number is unknown (e.g., after MTBSS
		  or MTSEEK).

       mt_blkno	  reports the block number  (zero-based)  within  the  current
		  file.	  This	value  is  set	to -1 when the block number is
		  unknown (e.g., after MTBSF, MTBSS, or MTSEEK).

   MTIOCPOS -- get tape position
       This request takes an argument of type (struct mtpos *) and reports the
       drive's	notion of the current tape block number, which is not the same
       as mt_blkno returned by MTIOCGET.  This drive must be  a	 SCSI-2	 drive
       that  supports the READ POSITION command (device-specific address) or a
       Tandberg-compatible SCSI-1 drive (Tandberg, Archive Viper, Wangtek, ...

	   /* structure for MTIOCPOS - mag tape get position command */
	   struct mtpos {
	       long mt_blkno;	 /* current block number */

       EACCES	     An attempt was made to write or erase a write-pro-
		     tected tape.  (This error is not  detected	 during

       EBUSY	     The  device  is  already  in use or the driver was
		     unable to allocate a buffer.

       EFAULT	     The command parameters point to memory not belong-
		     ing to the calling process.

       EINVAL	     An	  ioctl(2)   had  an  invalid  argument,  or  a
		     requested block size was invalid.

       EIO	     The requested operation could not be completed.

       ENOMEM	     The byte count in read(2) is smaller than the next
		     physical  block  on  the tape.  (Before 2.2.18 and
		     2.4.0-test6 the extra  bytes  have	 been  silently

       ENOSPC	     A	write  operation could not be completed because
		     the tape reached end-of-medium.

       ENOSYS	     Unknown ioctl(2).

       ENXIO	     During opening, the tape device does not exist.

       EOVERFLOW     An attempt was made to read or write  a  variable-
		     length  block  that  is  larger  than the driver's
		     internal buffer.

       EROFS	     Open is attempted with O_WRONLY or O_RDWR when the
		     tape in the drive is write-protected.

       /dev/st*	   the auto-rewind SCSI tape devices

       /dev/nst*   the nonrewind SCSI tape devices

       1.  When	 exchanging  data between systems, both systems have to
	   agree on the physical tape block size.  The parameters of  a
	   drive  after	 startup  are often not the ones most operating
	   systems use with these devices.  Most systems use drives  in
	   variable-block  mode	 if the drive supports that mode.  This
	   applies to most modern drives, including DATs,  8mm	helical
	   scan	 drives,  DLTs,	 etc.  It may be advisable to use these
	   drives in variable-block  mode  also	 in  Linux  (i.e.,  use
	   MTSETBLK  or MTSETDEFBLK at system startup to set the mode),
	   at least when exchanging data with a	 foreign  system.   The
	   drawback  of this is that a fairly large tape block size has
	   to be used to get acceptable data transfer rates on the SCSI

       2.  Many	 programs  (e.g., tar(1)) allow the user to specify the
	   blocking factor on the command line.	 Note that this	 deter-
	   mines the physical block size on tape only in variable-block

       3.  In order to use SCSI tape drives, the basic SCSI  driver,  a
	   SCSI-adapter	 driver and the SCSI tape driver must be either
	   configured into the kernel or loaded	 as  modules.	If  the
	   SCSI-tape driver is not present, the drive is recognized but
	   the tape support described in this page is not available.

       4.  The driver writes error messages to	the  console/log.   The
	   SENSE  codes	 written  into	some messages are automatically
	   translated to text if verbose SCSI messages are  enabled  in
	   kernel configuration.

       5.  The	driver's  internal  buffering allows good throughput in
	   fixed-block mode also with small read(2) and	 write(2)  byte
	   counts.   With direct transfers this is not possible and may
	   cause a surprise when moving to the 2.6 kernel.   The  solu-
	   tion	 is to tell the software to use larger transfers (often
	   telling it to use larger blocks).  If this is not  possible,
	   direct transfers can be disabled.


       The  file  drivers/scsi/README.st  or  Documentation/scsi/st.txt
       (kernel >= 2.6) in the Linux kernel  source  tree  contains  the
       most  recent  information about the driver and its configuration

       This page is  part  of  release	4.10  of  the  Linux  man-pages
       project.	  A  description  of  the  project,  information  about
       reporting bugs, and the latest version  of  this	 page,	can  be
       found at https://www.kernel.org/doc/man-pages/.

Linux				  2016-06-05				 ST(4)