Computers and computer science have been my field for many years. I'm
now retired, but still try to keep up. Even after this many years the
field still comes up with surprises on a regular basis.
I understand that DVD's are far less archival than CD's, something to
Maybe so and maybe not. DVDs are a two layer plastic sandwich with
the recording medium located between them. DVDs suffer from a
different failure mode when being handled, but they are rugged.
The problem with any "projected media life" which is all we have
available for both CDs and DVDs is "no one really knows" what the real
lifetime will be.
http://www.rogerhalstead.com/scanning.htm Might help some.
All, and I emphasize "all", optical media lifetimes are based on
either accelerated aging which is then interpolated to get the
projected life of the media, or "wishful thinking" and I'm not so sure
that a number of projected lifetimes haven't been developed in the
minds of those in the marketing departments.
The straight and honest answer is, "We do not know how long any of the
digital media will remain readable, or how long the data integrity
will remain intact."
Accelerated aging means we have to guess at what will cause
deterioration of the media. Sunlight, heat, and humidity are three
known issues, BUT some surprises have popped up. Some sort of
apparent fungus and delaminations. All you have to do is miss one of
the real life contaminates and your projected lifetime is out the
window.
do with their manufacture for video rather than data. The Delkin Gold
eFilm claims 300-year archivablilty. It's probably a trade-off (what
That 300 year figure would make me leery of those right off the bat.
They may be the best CDs on the market...and they may not. However a
300 year figure is highly unrealistic for several reasons.
1. Even with accelerated aging there is absolutely no way of
knowing the medial will remain viable that long. The accelerated
aging process may go on for months, or a couple of years, but beyond
that you have to make projections based on what are really limited
results. Plus you have to make the assumption you have taken into
account all the possible forms of failure due to age. The farther you
project the life beyond the test the larger the likely error. When
projecting lifetimes that are hundreds or thousands of times longer
than the test the figure gets closer and closer to becoming
meaningless.
2. A warranty is only a good as long as the "original" company
stays in business. They go under, some one buys them out, or they
declare the product obsolete and no longer supported and end of
warranty.
3. Storage media is evolving at a relatively fast pace. Rather
than the lifetime of the media, finding equipment to read it could
easily become a problem within a decade, or maybe two which is far
sooner than we'd expect the media to fail. The general consensuses is
we will most likely have to "refresh", or change media about once a
decade.
4. The dye layer is probably far more important than the gold
reflective layer as the information is contained within the dye layer.
Of course if the reflective layer were "unprotected" Aluminum it'd
most likely corrode away. Plus not all dyes are created equal.
isn't?): Pay now for more CD's and long-range archivability, or pay
For me it's not the price but the number. I have several hundred DVDs
which would translate into more than 1200 CDs and that becomes a
number too large to manage on a practical basis. Oops... I forgot the
"other stuff". The total DVDs is over 400 which equates to about 2,800
CDs. I have over 5 Terabytes on Hard Disks. That would be
unmanageable even on DVDs, but fortunately much of what has to be
backed up can be done in compressed form. Images OTOH are saved as
TIFFs and uncompressed which account for the 200 or so DVDs.
for fewer DVD's, but continual re-burning every 5 years to maintain
image integrity. I'm assuming the digital file is all that remains.
For 10, 20, or maybe even 30 years there probably isn't a nickel's
worth of difference between the two as far as lifetime, but again we
really don't know for sure beyond about 15 years. Nature has already
provided some surprises and we know that no storage medium lasts
forever.
Depending on the volume of photos you digitize the verification of the
data integrity can become prohibitive time wise in a few years. It is
after all, not a good idea to digitize, store the CDs or DVDs away and
expect to find them in good shape 10 or 20 years down the road without
checking them periodically for data integrity/readability.
So, how ever you choose to archive, I wish you luck
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com