From the April 2006 issue of Mediaware
Live Long and Prosper: Defining Disc Longevity
By David English
It's a simple question asked more and more by the public. How long will these recordable discs last? The short answer is that no one really knows. Not surprisingly, that answer isn't good enough for government archivists who want to commit vast amounts of information to digital storage. It also isn't good enough for families who want to preserve their irreplaceable photos and home videos. The public nervousness has intensified recently, following articles in the press that have played up the potential fragility and instability of recordable discs.
“Everyone recognizes this is an important area, because right now all we have are the individual claims of the manufacturers,” says Tony Jasionowski, senior group manager for Panasonic Corporation of North America . Jasionowski is a member of an ad hoc committee that is developing a methodology for evaluating the life expectancy of recordable discs. Given the name of ODAT (Optical Disc Archive Test), the committee was formed under the auspices of OSTA (Optical Storage Technology Association). ODAT is working with NIST (National Institute of Standards and Technology), as well as two organizations in Japan : DCAJ (Digital Content Association of Japan) and CDs21 Solutions. Some preliminary testing of recordable DVD discs is already underway.
Because it's too early to report results from the studies that ODAT is involved in, Jasionowski couldn't provide any definite conclusions. “There are indicators the media could last 100 years,” he explains. “It's not conclusive to say the results are a 100-year life, but there are indicators that show they could last a lot longer than 30 years.” That would be encouraging news for manufacturers, and it runs counter to press reports that DVD recordable media may last only 5 years.
ODAT hopes to forge an agreement for a large-scale testing project, which could eventually lead to some form of certification. “OSTA can't do it alone,” says Jasionowski. “We have to leverage the resources of other groups that already are doing it.” NIST, DCAJ, and CDs21 have environmental test chambers, “but no single organization has enough chambers or enough resources to do this project,” says Jasionowski. Through a comprehensive, standardized series of tests, the industry could develop procedures for the independent verification of its longevity claims. “That's the key: independent verification,” he explains. “We don't have that. And that's what we're working towards with these various groups.”
In December, OSTA, DCAJ, and CDs21 held a joint meeting in San Francisco. “We agreed collectively as three organizations that we should look at all the recordable DVD formats,” says Jasionowski. “That means DVD-R, DVD-RW, DVD+R, and DVD+RW, as well as DVD-RAM.” It's still early days for establishing the procedures for the large-scale tests. One issue being discussed is how to select the discs to be tested. “OSTA doesn't usually go to the manufacturers and request samples of media. Typically OSTA goes out with a budget and purchases various media types in the open market.”
NIST has used a similar approach for its ongoing study comparing the stability of different types of recordable discs. “We purchased several brands of optical media: DVD-R, DVD+R, DVD-RW, DVD+RW, CDR, and so on,” explains Oliver Slattery, a researcher for the Information Systems Division (ISD) at NIST. “We're aging them at various temperatures and humidities, and analyzing the data.”
The NIST study is a collaboration with the Library of Congress. “They have very extensive CD and DVD holdings,” says Slattery. “They mostly hold ROM media, but they may extend that to recordable media. They're very interested in how long that media will last, so they can better plan their retention strategies.” The study will take two years to complete. Their goals are “to better understand the life expectancy of optical media, to promote superior quality optical media, and to potentially influence manufacturing trends.”
NIST is currently testing hundreds of discs. “We have five DVD-R brands of 100 discs each, five DVD+Rs, two –RWs, two +RWs, and one ROM CD and DVD for comparison. We also have seven CD-R type brands, each of which includes over a hundred discs, because we're doing a number of different studies with them.”
The price range of the discs is relatively narrow, so NIST won't be able to correlate price with longevity. “When we started this study, there was no expensive media,” Slattery explains. “They were all pretty cheap. You couldn't buy expensive media even if you wanted it. More expensive products are available now that claim to be more durable and compatible, but we've already started the study. The results of our study will represent what general consumers would expect when they go into Best Buy, Staples, CompUSA, Wal-Mart, or wherever they get their media—without seeking anything special.”
A Moving Target
Long-term studies of consumer-based products have an inherent problem. A statistically valid study takes a long time to complete, but by the time the results are released, the materials and manufacturing processes will likely have improved. “That's an absolutely crucial issue for the manufacturers,” says Slattery. “They don't want to spend two years testing their media to certify it, because in two-years time, they would have gone through two or three generations of products.” He hopes that if the industry moves towards certification, the test procedures could become significantly shorter.
Slattery thinks NIST could make a lasting contribution by “coming up with a test methodology the industry could use either for self certification or for independent certification.” However, he doesn't see all media being tested this way. “Only the top-quality media would be certified.” It would too costly and time consuming to test media that isn't specifically formulated for a longer life.
The NIST tests are derived from the ISO 18927:2002 standard, with adaptations to ensure that suitable error rates and data points were obtained for recordable media. Initial testing, carried out in 2004 and 2005, indicated that the stress conditions and durations described in ISO 18927:2002 (minimum of 500 hours per aging cycle at increased temperature and humidity conditions) may be too harsh, with the result that very high error rates were obtained after one aging period. Instead, NIST adopted an approach whereby the incubation length for each aging cycle could be altered, depending on the error trends.
Based on NIST's previous humidity and temperature stress tests, Slattery can draw some preliminary conclusions. “In terms of compatibility, and in terms of getting good quality recordings, we found there wasn't that big a difference between any of the particular formats.” And how about the contradictory claims that DVD recordable discs may last only 5 years, or may last as long as 100 years? “From our initial study, we didn't calculate a lifetime, just because we didn't have enough information to make a claim. But we were able to monitor error rates after artificial aging. We found that some media are capable of lasting several tens of years, though we don't know what several tens of years actually is, but certainly longer than five or ten years. But we also found that other discs would probably be dead in under ten years. Our results tells both stories.”
While the effects of humidity and temperature are vital to understanding disc longevity, they're not the whole picture. “We know there are many factors at play,” says Slattery. “For example, the biggest thing that will destroy your disc is just the way you handle it.” Scratches and storage conditions are under the control of the user, not the manufacturer. “The recording itself is to an extent under the user's control, because they can make sure they have the right burner that matches that media.” Beyond the user's control is the construction, materials, and manufacturing processes, as well as the quality control used to produce the disc.
Because the manufacturer and consumer share responsibility for the longevity of any given disc, certification can't be handled on the package with just a simple logo. “I think there will be a disclaimer with whatever comes out,” says Slattery. “That this disc—if recorded properly, stored properly, and handled properly—whatever all that means—will last a very long time. Whether they're going to put a number on that or not, I'm not sure.”
Sidebar -- Certified Media: Imation and ISO 18927
OSTA and NIST are working towards a system of tests that could eventually lead to certification for disc longevity. But what about the short term? What can manufacturers use today to provide a seal of approval for media that's designed for a long life?
Imation wants to use the ISO 18927:2002 methodology. It's the “only industry accepted test procedure that is available right now for disc longevity testing,” says Jathan Edwards, a research specialist for Imation's product development lab. “It proscribes a test methodology, the number of samples, how to go about the calculation based on the statistical failure, rankings of the media, and how to calculate a lifetime with what kind of statistical confidence. It's a very comprehensive test.”
Why didn't the industry adopt this standard years ago when it was first ratified? The primary reason: It's a lot of work. “It requires at least five different environmental stress conditions with a statistical number of samples that you put in these environmental ovens,” explains Edwards. “You have to test them periodically through 3,000, 4,000, and 6,000 hours of environmental stressing. In many cases, the test cycle will take one to two years.” Another reason has been the rapid changes in manufacturing. “Every time you change groove geometry, dye type, reflector thickness—anything like that—you're basically reconstituting your media,” he says. “If you start an accelerating test on a 4x media, and it takes you two years to finish or complete the full cycle of testing, by the time you've finished your two years of lifetime testing, that 4x media is pretty much obsolete.”
The methodology allows manufacturers to characterize longevity as a precise number of years, which is how consumers want longevity measured and communicated. “The ISO test proscribes that, if you follow this procedure,” Edwards says. “They even suggest a lifetime expectancy statement and how it needs to be worded and properly couched with the right storage conditions, and so on.” Imation published the conclusions of its own ISO 18927 tests as part of a February 2 announcement. “With the results we have been able to show so far on our 52x CD-R and our 16x DVD-R media, we can arrive at lifetime expectancy terminations that exceed 50 years.”
Imation's accompanying “Life Expectancy Statement” goes into more details about what the test results indicate, including a stipulation that the ISO 18927 tests consider “only the effects of temperature and humidity,” and that the test regime “does not attempt to model degradation due to exposure to light, corrosive gases, containments, handling, improper storage or variations in the quality of the recording/playback system.” The statement also stipulates that the number of years is predicted with a 95-percent level of confidence, as determined by the ISO 18927 standard. That gives manufacturers some wiggle room from having to make an absolute guarantee that any given disc will last a specific number of years.
Imation plans to test market its ISO 18927 certified media to the government, and then will consider a possible migration path to the general consumer. The certified media will have a higher price. “There is a substantial amount of work that goes into making a product like that available and ensuring it has all the characteristics necessary to give customers the very highest level of confidence,” explains Steve Bradley, Imation's global product strategy manager.
What does Edwards think about the possibility that another testing standard might evolve from the work OSTA and NIST are doing? “That probably isn't a short-term solution,” he explains. “In the end, I suspect that—in order to be as statistically accurate as the current test—it will end up being just as elaborate a test as what we have right now.”
Sidebar -- From the Front Lines
Archivists in the U.S. government are helping to drive the industry toward longer lasting recordable media. But that's only half the equation. “They want some sort of guarantee from the manufacturer that there's going to be something around to play the discs on,” says Bernie Mitchell, president of the DVD Association. “We did a summit at NIST last year, which was all about next generation issues. The government loves the concept of HD-DVD and Blue-ray with its better capacity, and holographic with its even greater capacity. The government is salivating over these for preservation. But then they ask, is there going to anything to play it on in 100 years?” He says the government is pushing hard for the industry to listen to its concerns.
Mitchell doesn't see an easy solution to the problem, primarily because innovation is being driven by the consumer side of the market. “The government is saying, why don't you consider making a ‘government issue system' that you could charge more for,” explains Mitchell. “It wouldn't be a consumer product. It would leverage some of the consumer manufacturing capabilities perhaps, but it would satisfy the needs of the government. Those needs would be longevity of media, a robustness in the delivery device, some migration path in the future, and a reliability that the device would be around and continue to the supported at a governmental level. The unfortunate thing is that the people they're talking to about this are the consumer electronics companies who are concentrating on the mass consumer. Those companies do have government divisions, but to create what the government wants would mean developing a different kind of product. And that's not something they're eager to do.”
Sidebar -- Selling Longevity: TDK
If the industry were to adopt standards related to the life expectancy of recordable discs, how would the discs be marketed? “I'm hoping we don't end up with a number of different grade levels that allow a good, better, best assortment of how long discs are going to last,” says Bruce Youmans, vice president of marketing for TDK Electronics Corporation. “I would rather get it down to a point that's very simplified as to what the professional archivists are looking for, and what they can live with in terms of best practices. Then we can come up with a grade level that satisfies that, and use that certification to help the professional, as opposed to allowing consumer enthusiasts to have choices in terms of price points. Even the enthusiasts on the consumer side deserve to know very clearly what it is that archivists have chosen. Let that be the barometer.”
Could manufacturers use an expiration date similar what we see on bread and milk packaging? “You can't do that,” says Youmans. “Even if you did—and that's one of the options we have as marketers—you would still have to have a lengthy disclaimer, such as 50 years based on an ambient condition of 25 degrees centigrade. All that stuff loads it up a bit.”
TDK faces similar challenges in marketing its DURABIS hard coating. “We brand it as scratchproof and archival, so that they can understand there's something to the product that's worth looking into. After the interest is drawn by the name, they can go into the product packaging, or to the website, and take a look at what we're talking about. They have to draw the same conclusion without us making a specific statement, such as ‘guaranteed 100 years.'”
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