A while back I posted a request for a tutorial about cartridge tapes and then
summarized the replies. I continued to get more replies on this subject and
have compiled them into this summary. I'll repeat the original summary and
then append the new summary.
Daryl Crandall
The MITRE Corporation
(703) 883-7278
daryl@mitre.org
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ORIGINAL SUMMARY
# Date: Mon, 9 Apr 90 11:16:31 EDT
# From: Daryl Crandall <daryl@dash.mitre.org>
# Message-Id: <9004091516.AA07838@dash.mitre.org>
# To: sun-managers@dash.mitre.org
# Subject: 1/4 inch tape summary
# Status: R
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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."
###########################################################################
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)
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NEW SUMMARY:
I don't think you will find a 4 track cartrdige tape drive in
any Sun but an obsolete Sun2. (We happen to have one!) Of course, if
you have written 9 tracks on a tape, you won't be able to read 9 tracks
with a 4 track drive.
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One more thing. A 60 Meg tape on a 60 Meg drive will max out at ~47 Meg.`
Try: dd if=/dev/rroot of=/dev/TAPE bs=1k
and wait for the stats when it runs out.
47 Meg is what I got.
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----- Begin Included Message -----
> 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?
----- End Included Message -----
As far as I have experienced this is working ok. Just use mt -f fsf
and skip as many records as you want. However there is one problem
coming up occationally. There was a bug in the st driver in Sun OS 4.0.0
and the bug is still there in the patched st driver for SPARCstation1.
The problem is that when you add a record on a new tape, a second EOF mark
is written after this one to indicate that this is the end of tape. When
another record is written to the tape the second EOF mark is supposed to be
overwritten. This is not always so. When you try to read the records,
you always get the first one, but to get the second you have to try two times
to skip the second EOF mark or you must multiply your fsf parameter with two :-).
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Well, I considered responding to the original question, but thought that you'd
probably get better info from someone else. Seems you didn't... also, I have
now found a copy of the *good* info I had read awhile back on this subject.
I include it below, after a couple of comments to your summary. I'd make one
comment to the info I saved though, and that is that at least under 4.0 the
driver *can* detect QIC-11 vs QIC-24 when reading, i.e. it doesn't matter
whether you use rst0 or rst8 *when reading* (this is in fact documented in
st(4S)).
> Here is an incomplete table of densities and lengths:
>
> QIC-11 QIC-24 QIC-150
>
> 300' 32M ?? ??
>
> 450' 45M ?? ??
>
> 600' 65M 150M ??
I do believe that the capacity difference here (as well as the comment about
different densities you quote) is incorrect, i.e. the difference isn't due to
QIC-11 vs QIC-24 but to 4-track vs 9-track. Since Sun more or less switched
from 4-track,QIC-11 to 9-track,QIC-24, this confusion (which seems to be quite
widespread) is understandable.
> Still need clarification on device assignments (/dev/st0, /dev/st8) and
This is well documented in ST(4S) of 4.0, I think.
Hope this helps...
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About a year ago, John Gilmore submitted to Sun-Spots a well-written
description of cartridge tape formats. I've included it below. Save it
and spread it around.
Mike Jipping Internet: jipping@cs.hope.edu
Hope College BITNET: JIPPING@HOPE
Department of Computer Science Voice: Hey!
=========================================================================
>Date: Thu, 18 Aug 88 02:56:03 PDT
>From: hoptoad.UUCP!gnu@cgl.ucsf.edu (John Gilmore)
>Subject: Cartridge tape formats and sizes (/dev/rst0 versus /dev/rst8)
There seems to be massive confusion about cartridge tapes. It's really
simple combinations of three different parameters.
There are two variants of the mechanical tape drive -- 4-track and
9-track. The tracks are used like on an 8-track audio tape (run all the
way down the tape on one track, then mechanically slide the head up or
down and do another pass of the tape.) The 9-track version can store
9/4ths as much data as the 4-track version. The 9-track version will read
4-track tapes but the tapes it writes can be marginal for reading on
4-track machines, because the tracks are thinner. Mostly they work.
There are two variants of the tapes themselves. One is 450 feet long
(DC300XL style) and the other is 600 feet long (DC600A style). They use
different magnetic coatings because the tape has to be thinner to fit 600
feet into a cartridge. Some older tape drives can only read/write the 450
foot tapes because their heads can't cope with the new magnetic coatings.
There is a sense hole on the cartridge (up near the write protect tab)
that lets the newer drives figure out how to set up the head for this
particular tape. The actual end-of-tape sensing is done with small holes
punched in the tape itself, detected with an LED, a mirror in the
cartridge, and a photocell, so that works fine for either tape length.
There are two variants of the bit format that controllers record on the
tape. One is called QIC-11, the other is QIC-24. QIC-11 is the original
Archive format (Archive Corp. started the whole 1/4" streaming cartridge
business). When a standards committee got a hold of it, they changed it
(of course) to QIC-24. In both cases, the tape contains 512-byte blocks
of data with small headers on them. For QIC-11, the block number in the
header is 8 bits; for QIC-24, the number is 24 bits. That is essentially
the only difference between the two. It was changed because in unusual
error recovery situations it's possible for the tape to move more than 256
blocks (at 90 inches per second and 8000 bits per inch, things go by
quickly -- think about it) and the controller could lose track of where it
was on the tape. Both formats hold the same amount of data on a given
tape.
If you make up a table of this stuff, you start seeing some familiar
numbers:
Tape 450' 600'
Drive
4-track 20MB [no such drives used in Suns]
9-track 45MB 60MB
The hardware takes care of 4-track/9-track and tape size issues, so all
you have to specify in software is whether you want QIC-11 or QIC-24
formatting. /dev/rst0 is QIC-11 and /dev/rst8 is QIC-24. I linked them
to /dev/rst.qic11 and /dev/rst.qic24 so I could just do it without looking
it up.
I believe Sun should have made the tape driver software attempt to read
tapes in both QIC-11 and QIC-24 format, like reel-to-reel tape drives
which will read whatever density you throw at them. They didn't,
unfortunately, so if you try to read a tape that's in the other format, it
looks like a totally empty tape (you get a "no data" error). Just rewind
and try again with the other format. If you get "no data" in both
formats, you really have a blank tape (or one recorded in yet some other
random format).
There are a few other manufacturers who use QIC-24 tape drives; the IBM
PC/RT is one. Apollos may be another, I'm not sure. Very few of the IBM
PC 1/4" tape drives use QIC-24; they all went off in different directions.
I don't know of any current production machines that use QIC-11 only; it's
obsolete.
Sun used to make all their distribution cartridges in 4-track, QIC-11
format on 450 foot tapes [20MB], since they can be read by all Suns.
Starting with SunOS 4.0, they are now making Sun-4 tapes in QIC-24 on
9-track, 600 ft tapes [60MB] which reduces the number of tapes by a factor
of 3. I am not sure whether Sun-3 tapes have been switched, though I
think all Sun-3's can read 60MB QIC-24 tapes unless they were upgraded
from Sun-2's. However, older boot PROMs can't boot from a QIC-24 tape
(they never ask the tape controller to try QIC-24 mode, and it's too dumb
to do it itself), which is why you may need a boot PROM upgrade from Sun
Tech Support to boot SunOS 4.0 from 1/4" tape.
[I wrote the 'ar' driver for 1/4" tape on Sun-1's -- my first Unix driver,
and it was really bad -- and maintained the boot code for tape drives
through the first Sun-3's.]
John Gilmore
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I prepared the following fact sheet on both the 9-track tape unit which we
use, and the Sun cartridges.
The info on the 9-track tape drive was obtained from mtio(4), xt(4S) and a
fair bit of experimentation. If you are lucky, it may also be true for
your own mag tape drives.
The info on the cartridge tapes comes from mtio(4), st(S) and several
contributors to Sun-Spots [sorry, I've forgotten who sent what]. The
bottom line is that there is very little to choose between rst0 and rst8
for the amount of data you get on the tape. However, whichever you choose,
you won't be able to read the tape back on some other machines! Sun-Spots
also explained the problems of booting SunOS installation tapes - If I
remember correctly, the boot proms in the earlier Sun 3 workstations could
only read QIC-11 format. Sun in their wisdom supplied SunOS 4 in QIC-24
format, necessitating users to upgrade their boot proms.
___ ___ ___
Andrew Yeomans PSTN: 0442 230000 ext 3371 |XXX| |XXX| | |
Crosfield Electronics Ltd INTL: +44 442 230000 |XXX| |XXX| |___|
Three Cherry Trees Lane Fax: 0442 232301 ___ ___ ___
Hemel Hempstead UUCP: ajy@cel.uucp |XXX| | | | |
Hertfordshire or mcvax!cel!ajy@uunet.uu.net |XXX| |___| |___|
HP2 7RH ___ ___ ___
England .. all opinions are my own, etc. |XXX| |XXX| | |
'The network is the bottleneck' |XXX| |XXX| |___|
-------------------------- cut here -------------------------------------
Magnetic tape devices
---------------------
xt - Xylogics 472 1/2 inch tape controller
------------------------------------------
Device name Maj Min Rewind on close Density Block size
Fixed block size mode:
/dev/mt0 8 0 Rewinding 1600 bpi 2048 bytes
/dev/nmt0 =/dev/mt4 8 4 Non-rewinding 1600 bpi 2048 bytes
/dev/mt8 8 8 Rewinding 6250 bpi 2048 bytes
/dev/nmt8 =/dev/mt12 8 12 Non-rewinding 6250 bpi 2048 bytes
Variable block size (raw) mode:
/dev/rmt0 30 0 Rewinding 1600 bpi Variable
/dev/nrmt0 =/dev/rmt4 30 4 Non-rewinding 1600 bpi Variable
/dev/rmt8 30 8 Rewinding 6250 bpi Variable
/dev/nrmt8 =/dev/rmt12 30 12 Non-rewinding 6250 bpi Variable
For compatibility reasons, the non-rewinding devices can be accessed by
either of the two names given.
'tar' and 'dump' default to using /dev/rmt8 (rewinding).
'mt' defaults to using /dev/rmt12 (non-rewinding).
The tape density may only be changed when writing if the tape is at the
load point, and if the drive is set to 'host-selectable density'.
The actual recorded tape density is used when reading or when writing
other than at load point, and any attempts to set it (on the front panel
or by device name) are ignored. The density status lights show the
selected density, not the actual recorded tape density.
st - SCSI 1/4 inch cartridge tape
---------------------------------
Device name Maj Min Rewind on close Format Block size
/dev/rst0 18 0 Rewinding QIC-11 512*n bytes
/dev/nrst0 18 4 Non-rewinding QIC-11 512*n bytes
/dev/rst8 18 8 Rewinding QIC-24 512*n bytes
/dev/nrst8 18 12 Non-rewinding QIC-24 512*n bytes
There are two parameters to consider with 1/4 inch cartridge tapes.
One is the number of tracks (4 or 9), the other is the encoding format
(QIC-11 or QIC-24). QIC-11 uses 1 byte block numbers, while QIC-24 uses
3 byte block numbers. QIC-11 has fractionally greater tape density,
while QIC-24 is more robust.
Tapes written by a 4-track drive can be read on a 9-track drive.
Tapes written by a 9-track drive may sometimes be read on a 4-track
drive, but with no guarantee of success.
Old Sun-2 machines can only write 4-track QIC-11 tapes.
Newer Sun-2 machines can only write 9-track QIC-11 tapes.
Sun-3 machines can only write 9-track QIC-11 or 9-track QIC-24 tapes.
Andrew J. V. Yeomans
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We record something like 55 Meg on 600 ft tapes regularly.
The last person who claimed to have results like yours with dd discovered he
had inadvertently slipped a shorter tape in. However, I do admit that
wouldn't explain 47 Meg.
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I don't know if this is a repeat msg but:
The important difference in capacities seems to be related to the overhead
associated with small blocking factors.
Try it with bs=126 (= 63k) and things should improve.
I think the question was referring to the 'r' option of tar, which,
according to the man page, will "write the named files on the end of the
tarfile. Note: this option *does not work* with quarter-inch archive tapes."
Not that i've ever had any need to use this option. I'd just be curious to
know if any of the answers you got addressed this.
Just to further your confusion about tape drives (:->), I'll tell you
this interesting tidbit. A while ago one of the engineers here was
looking at two boxes of tape cartridges (we buy 3M carts, and they
come 5 to a box). One box had DC-600As in it, the other had DC-6150s.
As you probably know, the 600As are 60-megabyte types, and the 6150s
are 150 megabytes. Anyhow, he noticed that each box had a `Technical
Brief' written on the side; _both_ boxes briefs had this information:
CHARACTERISTICS
620 ft (189.0m)
12500 ftpi
550 oersted tape
ftpi stands for Flux Transitions Per Inch.
If you beleive those numbers, it looks like 6150s and 600As are
*exactly the same* tape! Now, I said to this engineer, "Surely 3M
wouldn't sell the same tape under two model numbers!" So, I stuck a
DC-600 in the drive, and gave my usual backup command to the computer
-- the same command that I use with the 6150s (if you're interested,
the command was `dump 5cfsu /dev/rst0 1500 /home'). The dump went
without a hitch; I then did a `restore t' to see if I could read the
tape, and of course, all the files were present. I didn't actually go
so far as to extract the contents of the files, but having been able
to extract the names makes me wonder if there is any difference at all
between the 600A and the 6150.
###########################################################################
More thanks to:
Len Evens <sysadm@gauss.math.nwu.edu>
stevej@Synopsys.COM (Steven Jukoff)
Sven Ole Skrivervik <svenole@vest.sdata.no>
per@erix.ericsson.se (Per Hedeland)
cel!ajy@uunet.uu.net (andrew yeomans)
sysadm@gauss.math.nwu.edu Tue Apr 10 11:46:28 1990
stevej@Synopsys.COM (Steven Jukoff)
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