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  lower-
       most  five  bits in the minor numbers are assigned sequen-
       tially in the order of detection. The minor numbers can be
       grouped  into  two  sets  of  four  numbers: the principal
       (auto-rewind) minor device numbers, n, and  a  "no-rewind"
       device  numbers, (n+ 128).  Devices opened using the prin-
       cipal 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/nst0l 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 the 32-bit architectures and  256  kB
       for  the 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 alloca-
       tion of 16 blocks of 128 kB succeeds).

       The  driver's internal buffer size is determined by a com-
       pile-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  neces-
       sary.  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() calls and remain in effect when  the
       device  is  closed  and  reopened.   Setting  the  options
       affects both the auto-rewind and the non-rewind 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. The tape location
       is   preserved  within  each  partition  across  partition
       changes.  The partition used for  subsequent  tape  opera-
       tions  is  selected with an ioctl. 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 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.

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 do don't contain any  informa-
       tion about the writing mode: when reading, the only impor-
       tant 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.

       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  follow-
       ing  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  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  non-zero  and  disable
                     compression  if  mt_count is zero. This com-
                     mand uses the MODE page 15 supported by most
                     DATs.
       MTEOM         Go  to  the  end  of the recorded media (for
                     appending files).
       MTERASE       Erase tape.
       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 non-zero, it gives the size
                     of the first partition and the second parti-
                     tion  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_PARTI-
                     TIONS 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       Retension 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  com-
                     mand  (device-specific  address)  or a Tand-
                     berg-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 documenta-
                     tion.
       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, 13 Boolean driver options,
               the buffer write threshold, defaults for the block
               size and density, and timeouts (only in kernels >=
               2.1).  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 logically 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   the    constants
               MT_ST_BOOLEANS,   MT_ST_SETBOOLEANS,  MT_ST_CLEAR-
               BOOLEANS, or MT_ST_DEFBOOLEANS logically 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 selec-
               tively cleared.

               The default options for a tape device are set with
               MT_ST_DEFBOOLEANS. A non-active 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 acti-
               vated  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  multi-volume
                      archives.
               MT_ST_ASYNC_WRITES  (Default: true)
                      When this options 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 com-
                      mand is issued.  Any errors reported by the
                      drive  will  be  held until the next opera-
                      tion.  This option must  be  set  false  to
                      write reliable multi-volume 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 mes-
                      sages  from  the  driver (effective only if
                      the driver was compiled with DEBUG  defined
                      non-zero).
               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,  com-
                      pression,  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 capabil-
                      ities 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   backwards   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  cor-
                      rectly  positioned  within  a file when the
                      device is closed.
               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  draw-
                      back  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.  Other-
                      wise  the  BSD semantics are used. The most
                      important difference between the  semantics
                      is  what  happens  when  a  device used for
                      reading is closed: in  SYSV  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 posi-
                      tion is not changed.
               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  ORed with the operation
               code.

               With kernels 2.1.x and later, the  timeout  values
               can  be  set with the subcommand MT_ST_SET_TIMEOUT
               or'ed with the timeout in seconds.  The long time-
               out  (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 wait-
               ing 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.

   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 cur-
                      rent medium type.
                  GMT_ONLINE(x): The last open() found the  drive
                      with  a  tape in place and ready for opera-
                      tion.
                  GMT_D_6250(x),   GMT_D_1600(x),   GMT_D_800(x):
                      This  "generic"  status information reports
                      the current  density  setting  for  9-track
                      1/2" tape drives only.
                  GMT_DR_OPEN(x):  The drive does not have a tape
                      in place.
                  GMT_IM_REP_EN(x): Immediate report  mode.  This
                      bit  is set if there are no guarantees that
                      the data has been 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.
       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_SOFT-
                  ERR_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 MTI-
       OCGET.   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
       EIO           The requested operation could  not  be  com-
                     pleted.

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

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

       EFAULT        The command parameters point to  memory  not
                     belonging to the calling process.

       ENXIO         During  opening,  the  tape  device does not
                     exist.

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

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

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

       ENOSYS        Unknown ioctl().

       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 non-rewind SCSI tape devices

AUTHOR
       The driver has  been  written  by  Kai  Mkisara  (Kai.Mak-
       isara@metla.fi)  starting  from a driver written by Dwayne
       Forsyth. Several other people have also contributed to the
       driver.

SEE ALSO
       mt(1)

       The file README.st in the kernel sources contains the most
       recent information about the driver and it's configuration
       possibilities.

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
       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  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) allow the user to specify the
       blocking factor on 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  automati-
       cally  translated  to  text  if  verbose SCSI messages are
       enabled in kernel configuration.

COPYRIGHT
       Copyright (C) 1995 Robert K. Nichols.
       Copyright (C) 1999 Kai Mkisara.

       Permission is granted  to  make  and  distribute  verbatim
       copies  of  this  manual provided the copyright notice and
       this permission notice are preserved on all copies.  Addi-
       tional  permissions  are  contained  in  the header of the
       source file.

Linux 2.0 - 2.2          January 18, 1999                       1