CdRot

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    "It is sometimes caused by poor manufacturing ... [but is thought to be] more commonly caused by poor handling. ... Part of the problem is that most people believe that it's the clear underside of the CD that is fragile, when in fact it's the side with the label. Scratches on the underside have to be fairly deep to cause skipping, while scratches on the top can easily penetrate to the aluminum layer. Even the pressure of a pen on the label side can dent the aluminum, rendering the CD unreadable. ... The worst part is that manufacturers frequently change the materials and manufacturing methods without notifying users. "When you go to a store and buy a DVD-R, and this goes for CD-R as well, you really don't know what you're getting," he [Fred Byers, NIST] says. "If you buy a particular brand of disc, and then get the same disc and brand six months later, it can be very different." This renders the frequently heard advice to buy name-brand discs for maximum longevity fairly moot, he says." -- paraphrased from CDs, DVDs not so immortal at cnn.com.

     


    Cdroms, and especially recordable cdroms, are not necessarily reliable for long term data storage. The Dutch PC-Active magazine has done an extensive CD-R quality test and concluded that in as little as 2 years some home recorded cd's may be unusable. Anecdotal reports vary widely. People report no problems with 5+ year old CD-Rs and many problems with 2 year old ones. Media Sciences says don't write on the label at all and recommend using the serial number instead if longevity is desired. Beware of the test results from accelerated aging processes - they very rarely match real life conditions without careful adjusting and correlation against realtime samples.

     

     


    "...scratching the top of the disk (or even any normal CD) is actually much worse than scratching the bottom. The data isn't stored on the label though, just very closely underneath it."
    "The problem with the really old CD-Roms is not a rumour. It was caused by some of the inks used in silk screening the label onto the finished CD. Over a period of 4+ years the ink would etch into the recording layer and cause data loss. In addition to light and temperature, the way you label your CD-R/RW media may effect its long term reliability as well. Remember that the recording layer is on the label side of the media."
    "...Don't rely on them. They can fade badly, even in darkness at a constant 65 degrees. ... The reason that I know this is that the company that I work for ... were using CD-Rs, and that is how I came to be familiar with how quickly they will fade. Kept at 40 degrees in darkness, they may last 15 years. Otherwise, count on 5 years. The military won't use them, the major oil companies won't use them, many state governments are issuing the same warnings that they issued a few years ago about Zips disks"
    "I work for THE major oilwell data archiver in Canada and we did extensive testing of media when we first started FIVE years ago. We have thousands of CD-Rs of raw and compressed data that are handled on an infrequent basis. All data problems to date have been the result of the user (dropped, scratched, oily finger prints, etc.), 70% are TDK, 5% Maxell, and 25% are Kodak. I should also mention that we make two copies of every disc and second is stored off-site in a vault, these have never failed."

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    You may want to check out the Canadian Conservation Institute's web site. They do their own accelerated aging tests and have published all the results of their findings on modern information carriers. It appears the life span depends on the type of CD (the quality of course) you use. I took a conservation of modern information carriers' course and have the course material here in the Heritage Office if you are interested. sue

    Susan Parsons, Collection Manager, Tr'ondek Hwech'in


    I did a prelim study of this a while ago when systems was considering options.

    the basic 2-copy solution where one of the copies was kept in argon gas and the other in usage. The argon gas displaces oxygen.

    Sony makes a disk that has no label on it, that is better generally than others. Labels and some kinds of markers can actually cause data loss. Not important for some things, but where long-term records are important, definitely an issue. There are CD-rom r/w drives that can actually cut a label into the disk itself with a laser... another approach is just to put a contents file on the disk and keep all labels to the cover of the disk for the argon jobs.

    Yes, it is a concern allright.

    Larry Kwiat (see below)

     

    Someone passed the following to me regarding CD-ROM life which was published in the newsletter of OCLC Pacific Network (PACNET):

    "A number of libraries have taken to heart various manufacturers' claims that CD-ROM discs will last twenty years. However, recent statements by the National Archives and Records Administration (NARA) have placed a damper on these extravagant estimates. NARA states that the expected lifespan of CD-ROMs is three to five years. A later report will provide more detailed information, but the main problem, according to Ken Thibodeau of NARA, is that the aluminum substrate on which the data is recorded is vulnerable to oxidation (breakdown in the presence of oxygen). This was confirmed in statements to NARA by representatives of 3M Corporation, the largest CD-ROM fabricator.

    The plastic that protects the substrate is oxygen permeable, so it provides no protections against the oxidation process. In fact, oxidation begins during the manufacturing process itself because there is no attempt to evacuate the air between the substrate and the plastic coating. It is claimed that preventing air from being introduced during manufacturing is cost prohibitive.

    The only coating presently available that could possibly protect against the oxidation process is glass. However, glass has other problems associated with it, including breakage. Additionally, the problem of evacuating air during manufacturing would probably remain a factor in the construction of glass-coated discs.

    Libraries that have considered eliminating paper subscriptions and substituting CD-ROM storage clearly need to re-evaluate their policies in the light of this information."

     


    In the long term this is a non-issue. In 5 years from now, you will be worried about your old CD's as much as you worry about data stored on your audio cassette tapes, 5 1/4" floppies, your 3 1/2" disks and your zip disks. Chances are, we will all be converting our data from CD's to the next technology to come around that has 100 times the capacity, which should be some time soon. At that point CD's will be going the way of the cassette, floppy and the zip disk. For example, about 6 months ago, I read about a blue wavelength laser CD or DVD coming along with 45 times the storage capacity. Who needs a CD holding a scant 700 Mb when you can be recording to a 30 Gb unit? Then 5 years after that, you will be upgrading to the next type of device.

    In answer to your question, I heard from one of our contractors that there is actually a CD certification system out there where different brands and makes of CD's are assigned a colour code based upon how reliable they are and what their life expectancy and warranty is. She warned me not to rely on CD's over the long term and strongly recommend I only buy CD's that are certified for a longer life under this system.

    On the other hand, I have been backing up my data on CD's since 1999 and have never experienced any problems reading the data. I have made sure to use a CD case instead of stacking CD's together, and store the CD's in containers out of daylight and sunlight. Now that I have read the information you sent, I may take the additional step of making a point to not write on the CD's with my permanent marker.

    That is about all I know on the CD issue.

    -- Tim Sellars

    Thanks for the new angle Tim. It bears thinking about, and knocks off a lot of the "doom and gloom" sparkle from the warning. I don't consider it a complete rebuttal though. Think of the family album - you aren't necessarily going to want to copy all of your data over with each new technology generation. Sometimes you just want to leave it on a dusty shelf for a few years before referring to it or passing it on to your descendants. -- Matt Wilkie

    When you mentioned albums that reminded me of another option that will likely be used more in the future - internet storage services. You will never need disks that only last a few years if you can store data at a service.

    I already use this method to store my digital photos - I have an on-line "family album". Much better than the hard version, as I can share it with family all over the world!

    Tim

     


    http://www.theregister.co.uk/2003/09/01/cdrs_deliver_degrading_experience/ (by way of Steve Lindley)

     

     

     

     

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