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

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 num-
       ber.  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 char-
       acteristics  (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 ar-
       chitectures.  In newer kernels the driver allocates the buffer in several parts if  neces-
       sary.   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 allo-
       cate 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 dy-
       namic buffer allocation with kernels older than 2.1.121 (this applies also to demand-load-
       ing 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 op-
       tions 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 par-
       tition switch is executed together with the next tape operation in order to avoid unneces-
       sary  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 sup-
       ported 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  de-
       termines 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 ex-
       actly.  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  be-
       fore  2.1.121 with buffering disabled or newer kernel) the write byte count must be a mul-
       tiple 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 opera-
       tions.  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 ar-
              gument 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  autoload-
              ers.   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  nega-
              tive  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  com-
              mand  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 ei-
              ther 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-spe-
              cific addresses are used.

       MTSETBLK
              Set the drive's block length to the value specified in mt_count.  A block length of
              zero sets the drive to 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  en-
              abled 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_DEF-
              BOOLEANS  bitwise  ORed  with  whatever combination of the following options is de-
              sired.  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 op-
              tions for it are defined the first time.  An activated device inherits from the de-
              vice 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 reli-
                     able multivolume archives.

              MT_ST_ASYNC_WRITES (Default: true)
                     When this option is true, write operations return immediately without  wait-
                     ing  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, po-
                     tentially 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 for-
                     ward 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 op-
                     tion 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).  Other-
                     wise, 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 be-
                     tween 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 file-
                     mark 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  de-
              fault 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 suc-
              cessful 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 in-
              dicates whether the drive requests cleaning.  The method used by the drive  to  re-
              turn  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 re-
              served.  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  den-
              sity  (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 MT-
                  SEEK 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 MT-
                  SEEK 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  re-
                  ports the current density setting for 9-track 1/2" tape drives only.

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

              GMT_IM_REP_EN(x):  Immediate  report mode.  This bit is set if there are no guaran-
                  tees 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-pro-
              tected.

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 oper-
           ating 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  vari-
           able-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 com-
           mand  line.   Note  that this determines the physical block size on tape only in vari-
           able-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  de-
           scribed 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  en-
           abled 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  configu-
       ration 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/.

Linux                                       2020-04-11                                      ST(4)

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