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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.  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 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  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
       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.  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.

   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  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  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 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 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  in
              kernels  2.1  and  later).  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 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 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  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_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 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_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 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 */
           };

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 2.2.18 and 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

       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 bus.

       2.  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.

       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 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

COLOPHON

       This page is part of release 5.10 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/.