ft -- Device Driver

Floppy-tape driver
/dev/ft

The device  driver ft supports floppy-tape drives.  It  has major number 4.
Minor-number    assignments   are   documented    in   the    header   file
/usr/include/sys/ft.h.

ft works  with QIC-40 and  QIC-80 drives from  Colorado, Archive, Mountain,
and Summit.  It offers the following features:

-> It uses  the bad-block  bitmap that  is written into  the first  two 32-
   kilobyte segments of tape at format time.

-> It uses standard QIC-40/QIC-80 Reed-Solomon error-correcting code (ECC).
   This technique uses three of every 32 blocks for error checking.  A tape
   block is one kilobyte long.

-> It supports no-rewind-on-close.  This feature permits you to concatenate
   several archives onto a single tape cartridge.

-> It performs auto-configuration for users who do not know if their drives
   use soft select  A or soft select B, or hard  select on unit 0, 1, 2, or
   3, with manual override.

-> It lets you configure the size of the tape buffer, from 64 through 4,064
   kilobytes.

-> It  reads from  and writes  to buffer  space rather  than going  to tape
   whenever possible.

-> It works with  partially formatted tapes.  Some formatting utilities let
   you select the number of tape  tracks to format, in case you do not want
   to take the time to format an entire cartridge.

-> It recognizes both 205-foot and 307.5-foot tapes.

-> It works  with the COHERENT  command tape with  the following arguments:
   rewind, retension, seek, status, and tell.

Please note that release 1.0 of ft has the following limitations:

-> It  does not  format  tapes.  For  now,  we suggest  that  you buy  pre-
   formatted  tapes,  or use  formatting  utilities  available under  other
   operating systems.

-> It does not  support the QIC-80 formats for MS-DOS  or UUCP file systems
   on tape.   These features do not  need to be part  of the device driver,
   and can be implemented by user-level applications.

-> It does  not perform data compression, as  documented in QIC-122.  Other
   forms of  data compression are presently  available under COHERENT, such
   as the -z option supported by the tape-archive command gtar.

-> The  device driver  is character-only: there  is no  corresponding block
   device for floppy tape.

-> It  does not  support 1,100-foot  tapes.   Although the  QIC-80 standard
   mentions this length, it is not in common use.

-> You cannot access a  floppy-disk drive from COHERENT while a floppy-tape
   drive is in  use.  Likewise, if a floppy disk  is in use -- for example,
   if it is mounted -- you cannot access the floppy-tape drive.

-> Although a QIC-80  drive can read a tape that  was formatted for QIC-40,
   it cannot write  to such a tape.  The cartridge  must be reformatted for
   QIC-80 before a QIC-80 drive can write to it.

See Also

device drivers,
fd,
ftbad,
gnucpio,
gtar,
tape

Notes

ft reports  any error that may  affect integrity of the  data.  If the same
block number  appears repeatedly in ft's warning messages,  it is a problem
on the  tape and the  block should be  in the bad block  list.  Because the
Reed-Solomon ECC used in ft allows the physical medium to spoil up to three
of every  32 one-kilobyte blocks  yet recover all  data, your data  set may
still be  recoverable despite these  errors; but you  should consider using
the command ftbad to add such blocks to your cartridge's list of bad blocks
before you again write data onto that cartridge.

The message:

    Get Reference Burst Failed

can occur  if you attempt to  back up to an unformatted  tape, or one who's
format is  unrecognizable.  If a backup fails with  this message, try using
another, formatted cartridge.

Systems  with a  very  slow CPU  (e.g.,  a 16-megahertz  80386SX) may  have
trouble  running ft  in multi-user  mode.  The  reason is  that floppy-tape
hardware does not have much intelligence  built into it, so the driver must
consume many  CPU cycles.  In such  instances, we suggest that  you back up
your system while in single-user mode (which is a good idea in any case).

© 2012 by Stephen A. Ness