8mm vs 4mm tape (again...)

8mm vs 4mm tape (again...)

Post by Steven D. Majews » Fri, 22 Jan 1993 10:36:11



Here is a contribution to the 8mm vs 4mm tape debate.
I'm sorry - I didn't have time to write up a summary when this talk
was fresh in my mind, but I figured better late than never.

On Tuesday, December 1, Dr. Robert Burns (Deputy Assistant Director
for Computing - Operations & Procurement) from NRAO ( National Radio
Astronomy Observatory ) gave a presentation on "Magnetic Tape Dilemma" --
discussing magnetic recording technologies, media (e.g. helical 8mm and DAT),
and devices.

This was set up partly because I had been badgering the Director of
Academic Computing with questions about 4mm vs. 8mm, and he said that
there were folks at NRAO who knew more about helical recording than
some of the manufacturers.

For raw data acquisition, NRAO has been on the "bleeding edge", and has
had to design and build their own systems. They built one of the
earliest helical scan digital tape systems based on video technology
( I thinks this was based on VHS - I'm not sure. ). They applied for
a patent, but were refused on the grounds that it was an "obvious"
modification. For their current systems, they have given up on
helical recording, and have again, custom built a fast high capacity
tape system. Since they are recording noisey raw data from several
radio telescopes, and the data will later be correlated together, they
are able to trade giving up error correction for increased capacity
and speed. ( Sorry - I didn't take notes on what the speed and
capacity of their system is! )

They also use "standard" tape systems for all of their processed
data, so there they have the same concerns of interchange/backup/archiving/
etc. that "normal" users do.

[ Note: I was particularly interested in the question of archiving,
 rather than backup of data. As someone in the audience noted:
 "most backups are never read". For archiving, I'm much more
 concerned about interchange between systems, standardization,
 date-shelf-life, tape wear, etc. - questions that don't arise
 much if you are concerned with backup, where the main criteria
 are speed and capacity. ]

Dr. Burns gave a talk that reinforced my initial predjudice for 4mm
vs. 8mm: he discussed the tape wrap angle and the likely greater
wear on 8mm tapes. He said that both systems are built on consumer
technology where the computer market is a tiny piece of the market.
But EXABYTE, in particular, has had problems with their vendors
changing their components out from under them. He said that with
EXABYTE tapes, of the same model number, but possibly different
years of manufacture, they have only had 90% success rate a
interchange. ( This sounded frightening! Is the any independent
verification of this claim from anyone out there? )

However, after these, and several other points that I though
weighed heavily in favor of DAT ( or QIC when it gets to higher
capacity ), Dr. Burns said that NRAO had decided to standardize
on 8mm and they are moving all of their old data from 9track to 8mm.

I asked him about this incongruity.

He said that:

(1) the main criterion was $$/MB. ( on one of his overheads was a
page from a report done at NRAO on this subject. ) That was easy
to quantify, and some of the other critera were harder to evaluate.

(2) They have deciede that they are probably going to have to
change technologies every 5 years or so, so they aren't real worried
about longer-term questions. They have a full-time person and a full
time system dedicated to copying 9 track tapes to 8mm - they project
that it will take 3 years or so to finish that task, and then they
plan to re-evaluate the technology and start again.

*Everybody* appears to have the same problems *managing* all of that
data. It was said that NASA has grant money to hand out if you
have a potential solution.

===============================================================================
 Steven D. Majewski                     University of *ia

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- only the letterhead has changed! ]

 
 
 

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