This one isn't quite so late. :)
Original question (paraphrasing/summarizing):
Is 8mm less reliable because of its higher data density? Or does
it make up for that by using a more robust error detection and
correction technique?
I got an overwhelming reply on this one; answers covered the full spectrum,
ranging from Chris Maio's <chris@boxhill.com> enclosure of an EXABYTE Corp.
technical bulletin, which optimistically claimed:
>
> It is entirely feasible to expect successful recovery of data
> archived on 8mm metal-particle media after a storage period of ten (10) or
> more years if reasonable diligence is applied throughout with regards to
> physical handling, cleanliness and environment.
>
[sure, it's feasible to expect just about anything! -ed.]
to the response from par@cs.tut.fi (Pauli Rasanen):
>
> 8mm tape will be reliable up to about six (6) months only. After that
> reliability is not guaranteed, though it could be possible to recover
> the data error-freely later too. Bits may leak through different tape
> layers on the reel.
>
> The 8mm tape was not meant originally to be a computer data storage.
> Very small loss of information with video data is not essential. You
> can still get the picture. But in the case of computer data, it is
> very crucial.
>
On the whole, I found the results of this inquiry rather inconclusive; a few
persons suggested that the only way to assure long-term recoverability was to
go Optical. This makes sense, but optical media is a lot more expensive.
I've included in this summary one instance of "real-life" experience and some
excerpts from Exabyte's Technical Bulletin (which I found quite educational).
It's a little long for inclusion in a summary (150 lines), but I'll happily
send out a copy to anyone who wants it.
+From: xilinx!cray!esch@uunet.UU.NET (Eric Schemmerling)
|
|Last year I was working for a 26 Billion dollar company which had similar
|concerns about storing their finacial data on 8mm. We had Exabyte Corp out
|to discuss this very issue. They have done accelerated time testing and
|have found the higher quality tapes (know as 'data 8' tape ) to have no
|errors after 7 years in a controlled enviornment... enviornments which
|are not controlled are unpredictable... 'data 8' tapes cost about 26.00 --
|Also, a note about data correction -- the way 8mm drives work lets them
|write then re-read the data as tape are being made. Normal tape heads do
|not have this capability.
|
|
+From: Chris Maio <chris@boxhill.com> [Exabyte technical bulletin]
| ...
| First of all, metal-particle 8mm media has a coercivity of 1500
| oersteds which is high enough to be very resistant to the transformation
| of recorded magnetic information when exposed to stray magnetic fields.
| Because of this, accidental erasure is highly unlikely. Even airport metal
| detectors, whether walk-through or hand held, do not affect information
| recorded on tape. X-rays and nuclear radiation (gamma rays) also have no
| effect.
| ...
| Physical damage to the medium is the most probable cause for
| unsuccessful recovery of shelf or archival storage information. Damage
| can be caused by bad equipment, a harmful environment and/or mishandling.
| The second most probable cause, contamination, can occur at any time
| throughout the storage process. And, contamination can either pre-exist
| on the tape or be created during the process.
| ...
| Carefully Select Candidate Tapes
| New tapes are not the best candidates for archival because they
| more-often-than-not contain some manufacturing-generated debris or will
| quickly self-generate it. ... candidate tapes should be used. They should
| have less than twenty (20) full passes, but more than four passes.
| ...
| Maintain operational and storage environments within the range of
| 17xC (62xF) to 24xC (75xF). The ideal storage temperature is at 18.3xC
| (65xF) at a 40% non-condensing relative humidity (R.H.). Keep the environment
| constant.
| ...
| Always store tapes on edge in their protective enclosures. Don't
| stack them flat or lean them against anything. Do not subject the tapes to
| high gravitational-force-type loads. In other words, don't drop them and
| don't stack excessive amounts of weight on top of them.
| ...
| Exercise the tapes once every twelve (12) months by running them from
| BOT to EOT and back to BOT at normal speed (not rewind).
| ...
+------------------------------------------------------------------------------
Note to Brian Styles - the 1/2" tapes at my site are mixed 1600 and 6250 BPI,
mostly 2400' length.
Thanks to all who had information or personal experiences to share:
Chris Maio <chris@boxhill.com>
joe@oilean (Joe McGuckin)
Brian Styles <brian@mrc-biostats-sun.cambridge.ac.uk>
jpl@allegra.att.com (John P. Linderman)
trr@lpi.liant.com (Terry Rasmussen)
etnibsd!vsh@uunet.UU.NET (Steve Harris)
aldrich@sunrise.Stanford.EDU (Jeff Aldrich)
ljmassa@radon.berkeley.edu (Lauren Massa-Lochridge)
bjk@pecos.rc.arizona.edu (Brian J. Kennedy)
B.Rea@csc.canterbury.ac.nz
par@cs.tut.fi (Pauli Rasanen)
xilinx!cray!esch@uunet.UU.NET (Eric Schemmerling)
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