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Annotation of coherent/a/usr/man/COHERENT/tape, revision 1.1.1.1

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                      3: tape                      Device Driver                      tape
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                      8: Magnetic tape devices
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                     10: 
                     11: This section gives a general explanation of COHERENT's use of in-
                     12: dustry-standard half-inch,  nine-track magnetic tape.  Exceptions
                     13: or additional information may be found in sections of this manual
                     14: describing particular devices.
                     15: 
                     16: A  tape volume  contains files,  each consisting  of one  or more
                     17: records and terminated by  a tape mark.  Two tape marks terminate
                     18: the  last file.   Tape  records may  vary in  length, but  cannot
                     19: exceed 2^16 bytes (2^15 is more practical).
                     20: 
                     21: Like  other block-oriented  devices, tape  units may  be accessed
                     22: through the  system's cooked interface or  through the raw inter-
                     23: face.  On a cooked device, seeking to any byte offset and reading
                     24: in any number  of bytes is possible.  It is  not possible to read
                     25: beyond the tape mark at the end of the current file.  All records
                     26: in the file  must be 512 bytes long, except  the last.  Write re-
                     27: quests must be made in  increments of 512 bytes, except the last.
                     28: A cooked tape may be mounted like a disk, but only as a read-only
                     29: file system.
                     30: 
                     31: A raw device bypasses the buffer cache, so I/O occurs directly to
                     32: or from the user's  buffer.  One write request generates one tape
                     33: record,  and one  read request returns  exactly one  record.  The
                     34: number of bytes read may be less than expected.  If the tape mark
                     35: is read,  a count of  zero is returned, but  the system positions
                     36: the tape  at the start of  the next tape file.   Seeking on a raw
                     37: device is ignored, and mounting is not allowed.
                     38: 
                     39: A unit cannot be opened if  it is off-line or already in use.  If
                     40: the write ring is absent,  the unit cannot be opened for writing.
                     41: Closing the  device has varying  effects, depending on  the minor
                     42: device opened  and whether the  device was opened  for reading or
                     43: writing.  In the case of reading, the tape is rewound; if the no-
                     44: rewind option was specified,  the tape advances to the next file.
                     45: In the case of writing, two tape marks are written at the current
                     46: position and  the tape  is rewound;  if the no-rewind  option was
                     47: specified, two tape marks  are written and the tape is positioned
                     48: between them.   When you close a device that  had been opened for
                     49: writing,  the tape  volume  ends at  the  current position;  data
                     50: beyond this point are undefined.
                     51: 
                     52: The following  device options exist, selected  by prefixes to the
                     53: device name:
                     54: 
                     55: hh     Read or  write  data at  high density.   The exact  density
                     56:      depends on the drive model,  but 1600 BPI (high) and 800 BPI
                     57:      (low) are typical.
                     58: 
                     59: nn    Do not rewind on close.
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                     63: 
                     64: COHERENT Lexicon                                           Page 1
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                     68: 
                     69: tape                      Device Driver                      tape
                     70: 
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                     72: 
                     73: rr    The device is raw.
                     74: 
                     75: Hard errors may occur during tape operation.  They include detec-
                     76: tion of the  end-of-tape (EOT) reflector, reading an unexpectedly
                     77: long record, or seeking a cooked tape into a tape mark.  After an
                     78: error, no  further operations may be performed  on the unit until
                     79: the program closes the  device and the operator rewinds the tape.
                     80: Soft parity errors may arise  due to dirt, bad tape or misaligned
                     81: heads.  On  writes, the driver attempts to  place the record fur-
                     82: ther along  the tape.   On reads,  the driver simply  rescans the
                     83: record.  After several  failures, the driver announces a hard er-
                     84: ror.
                     85: 
                     86: Most utilities  use generic device names, which  are links to the
                     87: actual device files appropriate for the site.
                     88: 
                     89: ***** Files *****
                     90: 
                     91: /ddeevv/mmtt -- Generic cooked tape device
                     92: /ddeevv/rrmmtt -- Generic raw tape device
                     93: 
                     94: ***** See Also *****
                     95: 
                     96: device drivers
                     97: 
                     98: ***** Diagnostics *****
                     99: 
                    100: Drivers may report errors to the console.
                    101: 
                    102: ***** Notes *****
                    103: 
                    104: Not every edition of COHERENT supports magnetic tape.
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                    130: COHERENT Lexicon                                           Page 2
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