At 08:28 AM 3/25/2005 -0500, Anonymous SET ARSCLIST DIGEST wrote:
>In his post Dave Nolan said,
>...writable CD/DVD copies are turning out to have SO many problems with
>longevity past 10 years that it seems that they are NOT good long-term
>archival storage media.
>Could you please elaborate on this.
We are essentially without data on longevity and even readability of media.
To some extent that is because hardware, formulations and manufacturing
processes are changing faster than testing can be done. Another factor is
that we lack viable test tools - particularly since validity of accelerated
life test is not quantified. Yet a third is the lack of incentive for the
manufacturer to establish those data, A fourth is that most media are
rebadged so that one has no consistency from one purchase to another.
That said - and recognizing that we have no more hard data on what follows
than on what went before - the most common reason for failure of a disc is
that it was poorly written to begin with. Poor writing is usually due to
mismatch between properties of the writer and the medium, especially at the
chosen speed. Thus, although a modern drive capable of writing at 24x will
write at 4x, whether the blank in question is capable of only 4x, 24x or
52x there is a good chance that that drive and that blank written at 4x
will give poor results. It would be wonderful to have a modern drive and
modern medium optimized together for writing at moderate speed; to have
that combination made available by a reliable vendor who could give
assurance of compatibility; and to have certification of some sort on at
least the quality of result that would obtain.
Don't hold your breath for such a vendor or for affordable product from
him. I have heard from many and tend to believe it true from my own results
that as fine a CD recorder as has been marketed to date is the Plextor 8x
writer (either model), particularly with SCSI interface. There is no doubt
that for archival purposes a caddy drive is wonderful protection for
writing and reading. As far as I know, the companies producing such
hardware have either dropped those lines as having no market or have gone
out of the business altogether.
For quality results, it is essential that the quality of write be
established for your writer(s), medium and speed. Properly, that should be
done with a battery of tests of the sort done by Media Sciences. For
practical reasons, BLER test equipment may be sufficient. Because I am an
amateur little concerned with longevity beyond my own lifetime, I find
error-rate tests with Infinadyne's Diagnostic and Inspector programs
sufficient; even the freeware CDSpeed will do the job adequately for some.
The bottom line is simple, though. A well written disc will read in any
modern player. It is true that error rates for shorter blanks are
substantially lower than those for longer ones and that errors tend to be
substantially more frequent toward the circumference of the disc - later in
the recording. But a well written "80-minute" disc will be more easily read
and will last longer than a poorly written 74 or even 63 (are they even
produced any longer?).
The similarities between recordable CDs and DVDs are more significant than
their differences, especially in -ROM applications. There is a complication
if you choose to write DVD-ROM on DVD+R - a bit which must be set correctly
for consistent reading. (I would appreciate it if someone knowledgable on
this would share specifics.) Otherwise, we have the same ignorance of
longevity, the same lack of correlation between package marking and
contents, the same issues of rebadging and consistency on the two media.
Fortunately, we also have the same ability to quantify write quality and
the same reason to hope that a well written disc will outlast one written
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