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:
- +o
- It uses the bad-block bitmap that is written into the
first two 32-kilobyte segments of tape at format time.
- +o
- 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.
- +o
- It supports no-rewind-on-close. This feature permits
you to concatenate several archives onto a single tape
cartridge.
- +o
- 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.
- +o
- It lets you configure the size of the tape buffer, from
64 through 4,064 kilobytes.
- +o
- It reads from and writes to buffer space rather than
going to tape whenever possible.
- +o
- 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.
- +o
- It recognizes both 205-foot and 307.5-foot tapes.
- +o
- 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:
- +o
- It does not format tapes. For now, we suggest that you
buy pre-formatted tapes, or use formatting utilities
available under other operating systems.
- +o
- 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.
- +o
- 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.
- +o
- The device driver is character-only: there is no
corresponding block device for floppy tape.
- +o
- It does not support 1,100-foot tapes. Although the
QIC-80 standard mentions this length, it is not in common
use.
- +o
- 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.
- +o
- 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
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.
A
The message:
Get Reference Burst Failed
A
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.
A
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).