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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,  the requested amount of data from the start of the block is returned and the
       rest of the block is discarded.

       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 of more pages of the user buffer
       not reachable by the SCSI adapter, etc.

       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  nonzero,  it
                     gives  the size of the first partition and the second partition contains the
                     rest of the tape.  If mt_count is zero,  the  tape  is  formatted  into  one
                     partition.   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
               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 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 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 only support 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 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-test6 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 kernel
       sources  contains  the  most  recent  information  about  the driver and its configuration
       possibilities.

COLOPHON

       This page is part of release 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.