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NAME

       st - SCSI tape device

SYNOPSIS

       #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);

DESCRIPTION

       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 detection.  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 principal (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 command 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.  Before
       Linux 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 constant which can be overridden with a
       kernel  startup  option.   In addition to this, the driver tries to allocate a larger temporary buffer at
       run time if necessary.  However, run-time allocation of large contiguous blocks of memory may fail and it
       is advisable not to rely too much on dynamic buffer allocation before Linux 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 Linux 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 determines 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 disabled.  Before Linux 2.1.121 allow writes with arbitrary byte count if
       buffering is enabled.  In all other cases (before Linux 2.1.121 with buffering disabled or newer  kernel)
       the write byte count must be a multiple of the tape block size.

       In  Linux  2.6, 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.

   Ioctls
       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 files).

       MTERASE
              Erase tape.  With Linux 2.6, 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 available for some HP autoloaders.  If mt_count
              is the constant 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 partition 0 contains the rest of the tape.  If  mt_count  is  zero,  the  tape  is
              formatted into one partition.  From Linux 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 supports 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-specific 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 variable block size mode.

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

       MTSETPART
              The active partition is switched to mt_count.   The  partitions  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 tape).

       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 superuser):

       MTSETDRVBUFFER
              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 since Linux 2.1).  A single  operation  can  affect
              only one item in the list below (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 medium.

              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_DEFBOOLEANS.  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 immediately 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 reliable 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 size.

              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  filemark.  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 necessary only when interchanging tapes
                     with some other systems.

              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 operation but causing the driver to lose track of the current  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 files.

              MT_ST_AUTO_LOCK (Default: false)
                     When this option is true, the drive door is locked when  the  device  file  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 depending  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
                     specification.

              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 Linux 2.6, 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 command.  If this is used,  the  driver
                     does  not  use  the  command.   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 performing 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  supports  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 System V semantics.   Otherwise,  the
                     BSD  semantics  are  used.   The  most  important  difference between the semantics 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 |
                          MT_ST_BUFFER_WRITES | MT_ST_ASYNC_WRITES;
                  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  Linux  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_TIMEOUT.  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  Linux  2.4.19  and  Linux 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_ST_DENSITY_SHIFT, and MT_ST_DENSITY_MASK.

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

              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 Tape.

              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 data.

              GMT_WR_PROT(x)
                     The drive is write-protected.  For some drives this can also mean that the drive  does  not
                     support 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 ½" 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
                     physically  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 since Linux 2.4.19 and Linux 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 */
           };

RETURN VALUE

       EACCES An attempt was made to write or erase a write-protected tape.  (This error is not detected  during
              open(2).)

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

       EFAULT The command parameters point to memory not belonging 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 Linux
              2.2.18 and Linux 2.4.0 the extra bytes have been silently ignored.)

       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.

FILES

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

       /dev/nst*
              the nonrewind SCSI tape devices

NOTES

       •  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 bus.

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

       •  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.

       •  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.

       •  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 solution 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.

SEE ALSO

       mt(1)

       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 possibilities