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Here is the summary to my posting about a tutorial on 1/4 inch tape drive
systems. I'll repeat the original question.
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Can somebody give me a quick lesson on the types of 1/4 inch cartridge
tape drives and cartridges. I've become terminally confused about
tape lengths, tape capacities, drive write densities, drive read densities,
automatic density switching, compatabilities, number of tracks, QIC-II,
QIC-24, QIC?? ... AAAARRRRGGGHHH!
Why can't tar add to the end of a file written on a 1/4 inch tape?
Why do you have to re-tension?
What is the past, present, and future of 1/4 inch tape drives?
Why is there air? :-
Daryl Crandall
The MITRE Corporation
7525 Colshire Drive
McLean, Virginia 22102
USA
daryl@mitre.org
(703) 883-7278
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Judging by the number of requests for the summary, There are apparently a
lot of people who are confused on this subject.
There are still several points that need to be cleared up, but I can not spend
much more time on this subject.
First of all there is a Sun document called:
"Sun Tutorial on 1/4 Inch Tape Drives" (Sun Part No: 800-1315-05)
This describes the physical tape mechanism. It does not describe the
industry's evolution of different tape lengths and drive types.
I won't go into the details in this document. Get it, it's worth it!
Other sources of documentation:
> Table 7-7 on page 84 of the System & Network Admin manual, shows
> the relation between some tape aspects.
> The manual pages for ST(4S) provide somewhat heavier type of info.
According to what I have gleaned in the last couple of days, cartridge tape
drives have either 4 or 9 tracks. I haven't gotten any information on
which types of drives have 4 and which have 9 tracks but according to
the Sun tutorial (above) "Tapes written on the 4-track drives can be read
reliably by the 9-track drive" (re-tension if you get errors). According to
the same source, tapes written on 9-track drives may (or may not) be readable
on a 4-track drive.
Tape re-tensioning is necessary relatively frequently to assure that the
tape moves smoothly across the heads and doesn't "chatter" or jerk causing
errors.
Data is recorded on the tape in serpentine tracks. i.e. starting from the
beginning of tape, track 1 is recorded forward until the physical end of
tape is reached and the recording direction is switched to record track 2
in reverse. This process continues until all available tracks have been used.
The erase head is the full width of the tape and is ONLY active during the
1st forward pass erasing ALL TRACKS on the tape.
> What is the past, present, and future of 1/4 inch tape drives?
>
> past: QIC-11, QIC-24, 300' tape, 450' tape
> present: QIC-150, 600' tape
> future: QIC-525, 1000' tape
> They're dead meat - but just like 2400' reels are still with us, 1/4
> inch cartridges will take awhile to decay away, reincarnating in new
> and seemingly wondrous forms at times.
Here is an incomplete table of densities and lengths:
QIC-11 QIC-24 QIC-150
300' 32M ?? ??
450' 45M ?? ??
600' 65M 150M ??
Still need clarification on device assignments (/dev/st0, /dev/st8) and
recording densities (QIC-11, QIC-24, QIC??)
> QIC-11 and QIC-24 are just different formats for writing on the tape.
> QIC-24 is newer, higher density, and has more secure head positioning
> - less susceptibility to misaligned heads screwing things up.
> QIC-11 and QIQ-24 write at the same density but with different
> error correction schemes. One is typically rst0 and the other rst8.
> The write heads don't generate fields strong enough to really
> overwrite existing data; they can only write on blank tracks.
> Why can't tar add to the end of a file written on a 1/4 inch tape?
> You can add to a cartridge tape on which you have a tar record.
> You just first use mt -f /dev/nrst8 fsf 1 (or nrst0 or whatever)
> to skip the first record. The `n' refers to the non-rewinding device.
> Use of /dev/rst8 would result in the tape rewinding after the skip.
Editor's note: I haven't tried this but I had a couple of responses indicating
that it would work. Feedback anyone?
Why is there air?
"We used it to make vacuum column tape drives work. Some of it got
out of the labratory by mistake."
"To fill my bicycle's tires."
"To blow up basketballs."
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Thanks to:
dan@breeze.bellcore.com (Daniel Strick)
ebersman@uunet.uu.net (Paul Ebersman)
chuckles@sne42e.orl.mmc.com (chuck strickland)
Len Evens <sysadm@gauss.math.nwu.edu>
martin@molndal.ericsson.se
stefan mochnacki <stefan@centaur.astro.utoronto.ca>
bit!markm (Mark Morrissey)
yamada-sun!root@nosun.West.Sun.COM (Super User)
jaf@cana.Inference.Com (Jose Fernandez)
This archive was generated by hypermail 2.1.2 : Fri Sep 28 2001 - 23:05:56 CDT