There've been a few questions on the mailing-list recently about the
shelf-life of various brands of CD-R storage media. The Technical
Advisory Service has compiled some relevant information about these
disks. It's important to note, however, that depositing and maintaining
digitised material on a compact disc, digital tape etc. should be part
of a broader strategy which protects not only the physical data, but
provides the relevant contextual documentation which will make that data
understandable by its later users.
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Information on CD-R storage media

Optical media can provide a reliable and relatively trouble-free storage
option for project data. As the device reader has no contact with the
disk itself, data loss is more likely to arise as a result of bad
handling/poor storage arrangements than mechanical failure. Indeed,
storage and handling will have a definite impact on the life of the
disks you purchase.


Some generic storage recommendations:

*keep storage and access areas free of smoke, dust, dirt and other
contaminants
*store magnetic media away from strong magnetic fields
*transport magnetic media in enclosures with space clearances of 50mm
*store in a cool, dry, stable and secure environment.
*acclimatise media before use
*use the highest quality media you can afford (the life of specific
media will be dependent on quality of manufacture)
*follow manufacturers' recommendations for labelling (avoid sticking
adhesive labels on disk surface or marking with pencil/biro)
*minimise handling and use of archival media and/or carefully record
access details
*implement refreshment procedures on a regular cycle within the
lifetime for archival storage identified by the manufacturer and/or
reliable independent sources
*implement migration procedures as necessary


Some Generic Figures for Lifetimes of Various Media:

                                storage conditions
Device                  25RH    30RH    40RH    50RH    50RH
                        10degC  15degC  20degC  25degC  28degC

-D3 magnetic tape       50yrs   25yrs   15yrs   3yrs    1yr
-DLT magnetic tape
cartridge               75yrs   40yrs   15yrs   3yrs    1yr
-CD/DVD                 75yrs   40yrs   20yrs   10yrs   2yrs
-CD-ROM                 30yrs   15yrs   3yrs    9mnths  3mnths

RH = % relative humidity

[figures taken from Beagrie, N. and Jones, M., Preservation Management
of Digital materials: a handbook (British Library, 2001)
ISBN 0-7123-0886-5]


Further Information:

There's a lot of information on the web about CD-R as a storage
technology. It's probably worth bearing in mind that most figures for
media longevity are based on manufacturers' own research (and range
anywhere from 10 to 200 years+). Until large-scale independent studies
are undertaken and published we have to rely on these figures, taken in
tandem with feedback from other users and the storage technology
community in general. Quality media from reputable, established
companies (such as Kodak, Mitsui, Mitsumi, Ricoh etc.) are likely to
provide the best storage and support options. The following websites
are informative starting points and have links to cater for most levels
of familiarity with the media.

> PADI website - http://www.nla.gov.au/padi/ - provides comprehensive
> links to relevant resources. Sections worth browsing include:
> storage <http://www.nla.gov.au/padi/topics/10.html>
> optical disks <http://www.nla.gov.au/padi/topics/53.html>
> physical formats <http://www.nla.gov.au/padi/topics/52.html>
>
> CD-R FAQ - http://www.fadden.com/cdrfaq/ - Andy Macfadden's site sets
> out to answer Frequently Asked Questions about CD-R technology in clear
> and comprehensive fashion.
> Sections worth browsing include:
> media <http://www.cdrfaq.org/faq07.html#S7>
> basic questions <http://www.cdrfaq.org/faq01.html#S1>
> further info on CD-R technology
> <http://www.cdrfaq.org/faq08.html#S8>
>
> Optical Storage Technology Association (OSTA) - http://www.osta.org/ -
> OSTA is an international trade body that promotes the use of writable
> optical technology for storing computer data and images. Lots of useful
> information and links to manufacturers (purchase information has
> strong US bias)
> Worth checking out FAQs <http://www.osta.org/technology/cdqa.htm>


Reminder:
Media with life expectancies of greater than 20 years will most likely
outlive their recording/reading systems. As changes/advances in
technology are inevitable, so a coordinated programme of refreshment
and migration will be essential to ensure continued readability of
recorded data.

----------------------
Peter Simpson
Development Officer
Arts and Humanities Data Service
King's College London
75-79 York Road
London SE1 7AW
[log in to unmask]
020 7928 7267