Russell McMahon writes:

> I am seriously interested in the ability to be "reasonably" confident
> about the long term archive quality of my optical media. My driving
> interest is my collection of over 100,000 digital photos,
> [ ... deletia ... ]
> If a reasonably fast, cheap & easy test could be achieved then one
> could buy a reasonable batch of a selected media (say 100+ quantity)
> and then test a small sample for performance. How large a sample was
> needed and how indicative this was of batch performance are things
> that should be able to be determined quite quickly by testing.

Unless you are dealing with a very large number of discs (in the
thousands) I'm not sure running your own tests would really be any
more effective than simply planning to re-archive the dataset every
few years.

There is also the problem of being able to obtain a quantity of media
that is guaranteed to have come from the same batch as your test
sample.  

> Here our new friends at Media Science suggest that any simplistic
> analysis won't be useful. AND that formatting errors are involved to a
> greater or lesser extent in over 50% of CD failures.
> http://www.mscience.com/cdrfail.html

This article implies that the design and construction of the drive has
a lot to play in the quality of the disk writes as well.  What the
this article doesn't mention, and what I rarely see talked about, are
the various write strategies required by different types of media.
Each of the different chemical compositions requires different laser
settings and write strategies.  Information about disk type is encoded
onto each disc, and used to a certain extent by both the firmware on
the drive as well as the PC burning software.  I think there are some
cases where if the drive doesn't know about the particular media type,
it has to guess.  I also think that some drives have the capability to
test-burn a portion of the disc to determine optimal settings via
trial and error.

I wish I could provide more details on this, but I have not been able
to find a lucid description for your average technical person who
isn't a materials scientist.  If anyone here *can* explain this in
greater detail, I for one would sure like to hear it!

But the upshot is certain: Some drives will make a much more optimal
burn than others, and in many (most?  all?) cases this comes down to
the software (and firmware) as much as the hardware itself.

-p.
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist