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International DVD Longevity Study: I call it the "The Canadian Study"
NOTE: "DVD-R discs" and "DVD movie discs" (below and in the study) are completely different kinds of DVD discs technologies.
"Movie DVD discs" Store data in the "metal (foil) layer" only. For this reason, "gold discs" were tested in "DVD Movie Discs" .
"DVD-R discs" Store data in the "dye (ink) layer" only. The metal (foil) layer of DVD-R discs "only reflects" light that is NOT blocked or filtered by the "dye (ink) layer".
Results of "aging" -- in DVD-R discs -- shows the "dye degrades" over time - resulting in loss of data.
Summary of The Study
DVD-Rs (Recordable DVDs)
Ten brands of single-sided/single-layered DVD-R discs were tested. Most discs were blue in appearance when viewed by the base side, but two were purple. It is suspected that either cyanine or azo dyes are being used in these discs; phthalocyanine is a very light green almost colorless dye. For the analysis, all the discs were grouped together. Most of the aged DVD-Rs showed minor changes in the dye color with aging. Two brands experienced significant fading, whereas another brand experienced irregular results (fading and darkening) from disc to disc. Only one disc brand suffered from delamination of the label adhered to the top of the disc. This did not lead to loss of the disc or performance problems. No delamination of the DVDs due to failure of the bonding adhesive was encountered.
Only 8% of the discs tested experienced a change in average PI of less than 280 and could be analyzed without problems after 84 days of aging. This indicates a significant amount of change and does not correlate well with the visual observations. It is possible that the dark color of the dye masks deterioration of the metal reflective layer.
MY INTERPRETATIVE OPINION AS A COMPUTER SCIENTIST and ARCHIVIST:
Another way to state this finding is, 92 percent of ALL DVD-R discs tested -- FAILED the longevity test -- due to discoloration in the "layer of dye". This discoloration in the layer of dye could possibly "mask" any visual observations in deterioration in the metal reflective layer.
I n layman's words, 11 out of every 12 DVD-R discs died in the longevity test! Because the "layer of dye" changed colors across the entire surface of most discs, the "metal layer" of the disc could NOT even be seen -- to evaluate the condition of the "metal alloy layer" (gold, silver, or whatever).
The longevity study -- a test of the effects of heat and light on the chemical properties of the DVD-R discs -- 'triggered" the light sensitive "layer of dye" to (KILL) change colors in 92 percent of the DVD-R discs tested. Changes in the "layer of dye" was so profound, blocking light so completely, that there was more "data error" than than there was "original data" on the DVD-R discs and the metal reflective layer could not be observed.
The Relative Stabilities of Optical Disc Formats (continued)
The disc format with the best survival percentage is the CD-R using the phthalocyanine dye. If longevity is a requirement when selecting a disc format, then the CD-R with phthalocyanine dye is a better choice than the other available CD or DVD formats. The silver metal reflective layer performed well, but if the environment is less than ideal, then a gold metal reflective layer will provide better stability. The one drawback is that the maximum capacity of the CD-R is only 700MB. This is a major problem for some, since collections of digital information are exponentially increasing in size.
The DVD-R format
currently provides about 4.7GB of storage (about 7 times more), but as illustrated in this study the DVD-Rs currently being produced are
showing the stability of the CD-R phthalocyanine discs. It is hoped that if the phthalocyanine dye is used for DVD-Rs in the future, then the discs will show the excellent aging stability of their CD-R counterpart.
The Relative Stabilities of Optical Disc Formats
There is a lot of uncertainty about the stability and longevity of optical disc formats. Manufacturers of these products do provide some data to support the long lifetime claims that they make. However, there is also anecdotal information indicating short lifetimes for optical discs.
This leads to confusion for individuals or organizations looking at possibly choosing optical discs for the archival storage of information. The purpose of this study is to help eliminate the confusion on the stability and relative longevities of optical disc formats. The focus of this research was not to determine lifetime values for individual disc brands. Instead, a variety of optical disc formats (audio CDs, CD-Rs, CD-RWs, DVD movie discs, DVD-Rs, and DVD-RWs) were subjected to accelerated aging at 80°C and 85% relative humidity in order to determine if and how these formats degraded. In addition, a relative stability ranking of the various optical disc formats was determined.
MY INTERPRETATIVE OPINION AS A COMPUTER SCIENTIST and ARCHIVIST:
BECAUSE YOU ASKED, "WHAT DOES THIS MEAN"?
The phrase, " a change in average PI of less than 280" , means there was a threshold for "passing the longevity test".
As I understand the study, the statistical method to find a "threshold for success or failure" was based on on a mathematical "moving average" ( called PI )
over any given 8 blocks (ECC Blocks) of data -- over the entire DVD-R platter.
The maximum threshold for" Success" was
1) "less than 280 errors" over ANY 8 blocks of data: AND
2) the DVD-R had to be "readable" from beginning to end.
Only 8% of the DVD-R disc (about 1 out of every 12 DVD-R discs on average) passed the" Stress test".
IMPORTATNT NOTE: Table 2: PI analysis of DVD movie discs aged for 84 days. Table 2 refers to
"DVD movie" discs -- NOT DVD-R discs.
In the actual report, which you can see in the PDF below, Table 2 is located in the middle of the "DVD-R disc" Section. However, Table 2 is referenced ONLY on the previous page -- discussing "DVD Movie disc" test results. Unless your actually read the "table title" you could assume your are reading about "DVD-R discs" -- not "DVD Movie discs". Since this table DOES include results on "GOLD DISCS", a person "skimming" the report could wrongly associate the longevity of "gold" "DVD movie discs" with "DVD-R discs".
BOTTOM-LINE: This is a VERY BAD longevity result -- as 11 out of ever 12 discs on average "died".
These results study results seem to have prompted the Longevity Study by NIST / Library of Congress to find a way to use "recordable DVDs" as "archive media". At the end of the NIST/LC study, the "method" of achieving longevity in "recordable DVD" disc proved to be beyond the the financial and technical means of 1) archive institutions, 2) corporations, and 3) private individuals. That is to say, building Disc Burning Stations (DBS) around ONE BRAND of "recordable DVD" -- staffing scientist to re-tune the "Disc Burning Station (DBS)" -- every few recording sessions -- what just not 1) financially and 2) practically an option for anyone.
INFLUENCE ON OTHER STUDIES:
This study was the foundation for The Longevity Problem addressed by the NIST/Library of Congress Study -- to see if the life of Optical Discs could be extended -- using very strict controls on both Disc Recorders and Disc Inventory. The NIST/Library of Congress study was successful in increasing longevity, however, the controls were too strict for routine archiving applications, and thus...
One month following the results of the NIST/LC study, the National Archives banned "recordable DVD discs" as an "archive medium" for use in the National Archives -- this website proves.
The Relative Stabilities of Optical Disc Formats by Joe Iraci
RESTAURATOR: International Journal for the Preservation of Library and Archive Material
Volume 26 - Number 2 - 2005