TC(4)                   COMMAND REFERENCE                   TC(4)



NAME
     tc - SCSI cartridge tape for 6130 System workstations

SYNOPSIS
     #include <sys/mtio.h>
     #include <box/tcreg.h>

DESCRIPTION
     The files /dev/tcnn refer to the SCSI cartridge tape
     interface.  The tapes have nine tracks of data in QIC-24
     format, providing up to 45Mb of storage.  The driver
     normally rewinds the tape when closed; this may be
     suppressed (for example, if you intend to add data to a
     tape) by using the /dev/ntc device instead of the /dev/tc
     device.

     Tapes are formatted with fixed length 512 byte blocks.  All
     reads and writes should be multiples of 512 bytes.  The
     streaming drive used in the tc device runs at 90 ips but
     takes several seconds to stop and restart.  For this reason,
     large reads and writes (up to 256kb at a time) are
     preferred.

     Reads and writes on tape are strictly sequential; seeks are
     ignored.  The tape may be rewound or spaced forward with the
     operations described in mtio(4).  Backward spacing is not
     allowed and attempts to backspace the tape may have peculiar
     results.

     The tc device may not be opened for simultaneous reading and
     writing.  Data may be written only at the beginning of the
     tape (erasing the old data) or at the end; existing data
     cannot be selectively erased or overwritten.  The driver
     writes a file mark when closed after writing.  Read returns
     a zero count when a file mark is read; the next read will
     fetch the first record of the next tape file.

DIAGNOSTICS
     tcnn: can't update cartridge tape

             An attempt was made to open the device for
             simultaneous read/write.

     tcnn: write protected

             An attempt was made to write on a write protected
             tape.

     tcnn: no tape

             An attempt was made to access a nonexistant tape
             drive or a drive without an installed tape



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TC(4)                   COMMAND REFERENCE                   TC(4)



             cartridge.

     tcnn: hard error, err=value<bits>

             An unrecoverable tape error occurred.  The error
             code is printed in hexadecimal with the bits
             symbolically decoded.  This message is printed on
             the system console.

RETURN VALUE
     Read(2) returns zero at a file mark.

     If an error occurs, the call returns -1 and one of the
     following values is left in errno:

     [ENODEV]    The named device doesn't exist, or you have
                 attempted to open a write-protected tape for
                 writing.

     [EBUSY]     Some process has opened the device.  No
                 additional opens are allowed until the current
                 user closes the device.

     [ENXIO]     You have attempted to write past the end of the
                 tape.

     [EIO]       An unrecoverable read or write error has
                 occurred.

CAVEATS
     Programs which were written specifically for nine-track
     magtape may not work on cartridge tape because of the fixed
     block size.  Other programs should be modified to buffer a
     reasonable amount of data with each write.

     New tapes, tapes which have been in storage, or tapes which
     have been exposed to temperature or humidity changes should
     be retensioned twice before use.  (The mt command provides
     an easy way to do this.) Failure to do this may result in
     unrecoverable read or write errors.

SEE ALSO
     cpio(1), dd(1), mt(1), tar(1), mtio(4), dump(8), restore(8).












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