James, in the mid-1990s, Dr. John W.C. Van Bogart, National Media
Laboratory, carried out considerable research on this topic.
Here are some excerpts from a presentation titled (in part) "How Long do
Digital Storage Materials Last?".
"The prevalence of media vendors, hardware suppliers, and tape
formulations make it impossible to come up with a single LE [Life
Expectancy] number that is valid for a given media at a specified
storage condition. Furthermore, media may fail for reasons other than
those considered when deter-mining the indicated LE values. As such, the
LE numbers on subsequent charts truly represent an educated guess at
this point." (Unfortunately, I don't have the charts--FJG)
"Keep in mind that LE values are similar to "mile per gallon" ratings
for automobiles -- "your actual mileage may vary" depending on the
number of times the tape is accessed during its life, the quality of the
conditions in which it is stored, and the care with which it is
handled/shipped."
"Cooling tape results in the slowing of the chemical processes which are
degrading the tape. Drier conditions reduce the amount of water absorbed
by the tape and also reduce the rate and ultimate extent of binder
hydrolysis."
"One point that this chart makes is that slightly higher humidities can
be tolerated at lower sto-rage temperatures for the same level of binder
degradation. It also shows the benefits of lower temperature and
humidity storage."
"The chart also demonstrates that the life expectancy of magnetic tape
can be significantly in-creased by slightly lowering the temperature and
humidity of storage. Life expectancies of 10, 17, and 28 years are
estimated for storage conditions of 72 F & 50% RH, 68 F and 40% RH, and
65 F & 30% RH, respectively. In these examples, both the humidity and
temperature have been reduced simultaneously. However, it is not
necessary to reduce both to see a benefit in media longevity. Either the
temperature or humidity can be reduced with benefit to the media."
"Media quality can vary appreciably from vendor to vendor. Also vendors
have good manufacturing days and bad ones. Therefore, a range of life
expectancies is provided (shown in yellow) to consider these variation
in media quality."
" Digital tape and disk media require special hardware in order to be
read. Even if the media survives for 50 years or more, the technology
needed to read the data may not survive for more than 10 or 20 years.
Thus, the life of a digital archive may be limited by obsolescence of
the drive hardware rather than the stability of the media."
"You can currently purchase WORM disks which are guaranteed for 100
years. However, considering the explosive growth of CD-ROM and CD-R
technologies, it is doubtful that WORM technology will be viable in 10
more years [this was written in 1996]. WORM disks will undoubtedly
outlive WORM technology."
Best regards.
Fred
===================================================================
Frederic J. Grevin
Deputy Commissioner and Chief Information Officer
The City of New York,
Department of Records
Email: [log in to unmask]
Land phone: 212.788.8615
Cell phone: 347.436.5360
Fax: 212.788.8614
www.nyc.gov/records
31 Chambers Street
New York, NY 10007
USA
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