NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | FILES | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       st - SCSI tape device

SYNOPSIS         top

       #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         top

       The st driver provides the interface to a variety of SCSI tape
       devices.  Currently, the driver takes control of all detected devices
       of type “sequential-access”.  The st driver uses major device number
       9.

       Each device uses eight minor device numbers.  The lowermost five bits
       in the minor numbers are assigned sequentially in the order of
       detection.  In the 2.6 kernel, the bits above the eight lowermost
       bits are concatenated to the five lowermost bits to form the tape
       number.  The minor numbers can be grouped into two sets of four
       numbers: the principal (auto-rewind) minor device numbers, n, and the
       “no-rewind” device numbers, (n + 128).  Devices opened using the
       principal device number will be sent a REWIND command when they are
       closed.  Devices opened using the “no-rewind” device number will not.
       (Note that using an auto-rewind device for positioning the tape with,
       for instance, mt does not lead to the desired result: the tape is
       rewound after the mt command and the next command starts from the
       beginning of the tape).

       Within each group, four minor numbers are available to define devices
       with different characteristics (block size, compression, density,
       etc.)  When the system starts up, only the first device is available.
       The other three are activated when the default characteristics are
       defined (see below).  (By changing compile-time constants, it is
       possible to change the balance between the maximum number of tape
       drives and the number of minor numbers for each drive.  The default
       allocation allows control of 32 tape drives.  For instance, it is
       possible to control up to 64 tape drives with two minor numbers for
       different options.)

       Devices are typically created by:

           mknod -m 666 /dev/st0 c 9 0
           mknod -m 666 /dev/st0l c 9 32
           mknod -m 666 /dev/st0m c 9 64
           mknod -m 666 /dev/st0a c 9 96
           mknod -m 666 /dev/nst0 c 9 128
           mknod -m 666 /dev/nst0l c 9 160
           mknod -m 666 /dev/nst0m c 9 192
           mknod -m 666 /dev/nst0a c 9 224

       There is no corresponding block device.

       The driver uses an internal buffer that has to be large enough to
       hold at least one tape block.  In kernels before 2.1.121, the buffer
       is allocated as one contiguous block.  This limits the block size to
       the largest contiguous block of memory the kernel allocator can
       provide.  The limit is currently 128 kB for 32-bit architectures and
       256 kB for 64-bit architectures.  In newer kernels the driver
       allocates the buffer in several parts if necessary.  By default, the
       maximum number of parts is 16.  This means that the maximum block
       size is very large (2 MB if allocation of 16 blocks of 128 kB
       succeeds).

       The driver's internal buffer size is determined by a compile-time
       constant which can be overridden with a kernel startup option.  In
       addition to this, the driver tries to allocate a larger temporary
       buffer at run time if necessary.  However, run-time allocation of
       large contiguous blocks of memory may fail and it is advisable not to
       rely too much on dynamic buffer allocation with kernels older than
       2.1.121 (this applies also to demand-loading the driver with kerneld
       or kmod).

       The driver does not specifically support any tape drive brand or
       model.  After system start-up the tape device options are defined by
       the drive firmware.  For example, if the drive firmware selects
       fixed-block mode, the tape device uses fixed-block mode.  The options
       can be changed with explicit ioctl(2) calls and remain in effect when
       the device is closed and reopened.  Setting the options affects both
       the auto-rewind and the nonrewind device.

       Different options can be specified for the different devices within
       the subgroup of four.  The options take effect when the device is
       opened.  For example, the system administrator can define one device
       that writes in fixed-block mode with a certain block size, and one
       which writes in variable-block mode (if the drive supports both
       modes).

       The driver supports tape partitions if they are supported by the
       drive.  (Note that the tape partitions have nothing to do with disk
       partitions.  A partitioned tape can be seen as several logical tapes
       within one medium.)  Partition support has to be enabled with an
       ioctl(2).  The tape location is preserved within each partition
       across partition changes.  The partition used for subsequent tape
       operations is selected with an ioctl(2).  The partition switch is
       executed together with the next tape operation in order to avoid
       unnecessary tape movement.  The maximum number of partitions on a
       tape is defined by a compile-time constant (originally four).  The
       driver contains an ioctl(2) that can format a tape with either one or
       two partitions.

       Device /dev/tape is usually created as a hard or soft link to the
       default tape device on the system.

       Starting from kernel 2.6.2, the driver exports in the sysfs directory
       /sys/class/scsi_tape the attached devices and some parameters
       assigned to the devices.

   Data transfer
       The driver supports operation in both fixed-block mode and variable-
       block mode (if supported by the drive).  In fixed-block mode the
       drive writes blocks of the specified size and the block size is not
       dependent on the byte counts of the write system calls.  In variable-
       block mode one tape block is written for each write call and the byte
       count determines the size of the corresponding tape block.  Note that
       the blocks on the tape don't contain any information about the
       writing mode: when reading, the only important thing is to use
       commands that accept the block sizes on the tape.

       In variable-block mode the read byte count does not have to match the
       tape block size exactly.  If the byte count is larger than the next
       block on tape, the driver returns the data and the function returns
       the actual block size.  If the block size is larger than the byte
       count, an error is returned.

       In fixed-block mode the read byte counts can be arbitrary if
       buffering is enabled, or a multiple of the tape block size if
       buffering is disabled.  Kernels before 2.1.121 allow writes with
       arbitrary byte count if buffering is enabled.  In all other cases
       (kernel before 2.1.121 with buffering disabled or newer kernel) the
       write byte count must be a multiple of the tape block size.

       In the 2.6 kernel, the driver tries to use direct transfers between
       the user buffer and the device.  If this is not possible, the
       driver's internal buffer is used.  The reasons for not using direct
       transfers include improper alignment of the user buffer (default is
       512 bytes but this can be changed by the HBA driver), one or more
       pages of the user buffer not reachable by the SCSI adapter, and so
       on.

       A filemark is automatically written to tape if the last tape
       operation before close was a write.

       When a filemark is encountered while reading, the following happens.
       If there are data remaining in the buffer when the filemark is found,
       the buffered data is returned.  The next read returns zero bytes.
       The following read returns data from the next file.  The end of
       recorded data is signaled by returning zero bytes for two consecutive
       read calls.  The third read returns an error.

   Ioctls
       The driver supports three ioctl(2) requests.  Requests not recognized
       by the st driver are passed to the SCSI driver.  The definitions
       below are from /usr/include/linux/mtio.h:

   MTIOCTOP — perform a tape operation
       This request takes an argument of type (struct mtop *).  Not all
       drives support all operations.  The driver returns an EIO error if
       the drive rejects an operation.

           /* Structure for MTIOCTOP - mag tape op command: */
           struct mtop {
               short   mt_op;       /* operations defined below */
               int     mt_count;    /* how many of them */
           };

       Magnetic Tape operations for normal tape use:

       MTBSF         Backward space over mt_count filemarks.

       MTBSFM        Backward space over mt_count filemarks.  Reposition the
                     tape to the EOT side of the last filemark.

       MTBSR         Backward space over mt_count records (tape blocks).

       MTBSS         Backward space over mt_count setmarks.

       MTCOMPRESSION Enable compression of tape data within the drive if
                     mt_count is nonzero and disable compression if mt_count
                     is zero.  This command uses the MODE page 15 supported
                     by most DATs.

       MTEOM         Go to the end of the recorded media (for appending
                     files).

       MTERASE       Erase tape.  With 2.6 kernel, short erase (mark tape
                     empty) is performed if the argument is zero.
                     Otherwise, long erase (erase all) is done.

       MTFSF         Forward space over mt_count filemarks.

       MTFSFM        Forward space over mt_count filemarks.  Reposition the
                     tape to the BOT side of the last filemark.

       MTFSR         Forward space over mt_count records (tape blocks).

       MTFSS         Forward space over mt_count setmarks.

       MTLOAD        Execute the SCSI load command.  A special case is
                     available for some HP autoloaders.  If mt_count is the
                     constant MT_ST_HPLOADER_OFFSET plus a number, the
                     number is sent to the drive to control the autoloader.

       MTLOCK        Lock the tape drive door.

       MTMKPART      Format the tape into one or two partitions.  If
                     mt_count is positive, it gives the size of partition 1
                     and partition 0 contains the rest of the tape.  If
                     mt_count is zero, the tape is formatted into one
                     partition.  From kernel version 4.6, a negative
                     mt_count specifies the size of partition 0 and the rest
                     of the tape contains partition 1.  The physical
                     ordering of partitions depends on the drive.  This
                     command is not allowed for a drive unless the partition
                     support is enabled for the drive (see
                     MT_ST_CAN_PARTITIONS below).

       MTNOP         No op—flushes the driver's buffer as a side effect.
                     Should be used before reading status with MTIOCGET.

       MTOFFL        Rewind and put the drive off line.

       MTRESET       Reset drive.

       MTRETEN       Re-tension tape.

       MTREW         Rewind.

       MTSEEK        Seek to the tape block number specified in mt_count.
                     This operation requires either a SCSI-2 drive that
                     supports the LOCATE command (device-specific address)
                     or a Tandberg-compatible SCSI-1 drive (Tandberg,
                     Archive Viper, Wangtek, ...).  The block number should
                     be one that was previously returned by MTIOCPOS if
                     device-specific addresses are used.

       MTSETBLK      Set the drive's block length to the value specified in
                     mt_count.  A block length of zero sets the drive to
                     variable block size mode.

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

       MTSETPART     The active partition is switched to mt_count.  The
                     partitions are numbered from zero.  This command is not
                     allowed for a drive unless the partition support is
                     enabled for the drive (see MT_ST_CAN_PARTITIONS below).

       MTUNLOAD      Execute the SCSI unload command (does not eject the
                     tape).

       MTUNLOCK      Unlock the tape drive door.

       MTWEOF        Write mt_count filemarks.

       MTWSM         Write mt_count setmarks.

       Magnetic Tape operations for setting of device options (by the
       superuser):

       MTSETDRVBUFFER
               Set various drive and driver options according to bits
               encoded in mt_count.  These consist of the drive's buffering
               mode, a set of Boolean driver options, the buffer write
               threshold, defaults for the block size and density, and
               timeouts (only in kernels 2.1 and later).  A single operation
               can affect only one item in the list 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
                      support only 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         top

       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         top

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

       /dev/nst*   the nonrewind SCSI tape devices

NOTES         top

       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         top

       mt(1)

       The file drivers/scsi/README.st or Documentation/scsi/st.txt (kernel
       >= 2.6) in the Linux kernel source tree contains the most recent
       information about the driver and its configuration possibilities

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       This page is part of release 4.07 of the Linux man-pages project.  A
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Linux                            2016-06-05                            ST(4)