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How To Verify CD-R Data Retention Over Time?
Peter (Professor) Fo writes "I've recently had two CD-Rs reported to me as faulty which are just 3 years old. This is worrying — I suspect the failure rate for this batch could be 10%. When researching CD longevity there is old and unreliable information; pious 'how to cosset your discs so they last 100 years' blurb; and endless discussions of what sort of dye to use, don't use cheap media, burn slower (or don't), but not much by way of hard facts besides there's a lot of data loss going on.
Does anyone know of a generic utility (win or *nix would suit me) that can map sector readability/error rates of CDs? I'd like to measure decay over time in my environment with my media and my other variables; and I expect others would too."
You should probably try dvdisaster. it can test media, and can create (on disk or external) redundancy data, which can be used to recover later.
It's also open source, so you could probably coerce it to export some more information
The following tool allows you to track the failure rate of your media, and allows you to recover the files and replace the cd/dvd when it starts failing. http://hardware.slashdot.org/article.pl?sid=08/08/03/197254
I work with CD/DVD and related technology as a profession. I analyze, QC, and mass duplicate media by the thousands for extreme and critical field use, every day. My best advice to you is to use Taiyo-Yuden (TY) media, always. I've seen mixed results and bad burns from Mitsui and MAM-A gold, Kodak, and the like. The TY dye type has a proven longer longevity than any other so far. I also suggest burning all of your audio CD's at 16X, this affect what's called single-beam readers. Also, it insures higher integrity of the burn. Burn 16X DVD's at 8X to increase the write integrity.
What others say about is CDCheck is true, use it along with this advice. Use Plextools Pro on a PX-716 drive if you can find one. It seems to be more accurate than Nero tools. Use Plextools to check the C1, C2, and CU rates. If the graph is half-way to the top of the reading, back that disc up. As cheap as media is, I suggest burning more than one copy, storing the image on an external archive hardrive. When burning, don't use overburning. You lose some integrity for error correction.
Store your media in a cool dry place, on it's side. Avoid humidity, light, and heat when you can. Remember, the best analysis tools in the industry are very expensive for individuals. Take a look at CATs if you are interested in learning more about optical media testing. Best wishes!
Short of an electron scanning microscope, the only way to do it is to hook an oscilloscope directly on to the test points within the drive itself and measure signal levels. This will allow you to measure one or both of: Degradation of the laser optics, degradation of the media. It's anyones guess as to which is which :-)
To make things a little more accurate, you should use several drives to test the media. The drives could benefit from being locked away until such a time as they are needed to repeat the tests. Mix in a few new drives when you do actually make your tests in future as well.
You're getting a couple different processes confused - writable-once and re-writable media are two very different things.
ReWritable discs ONLY (CD-RW, DVD+/-RW), use a layer of a metal alloy that undergoes a reversible phase change (crystalline/amorphous) when written (heated and cooled by different amounts at different rates). This phase change produces a very small change in reflectivity, to allow reading.
Recordable (CD-R, DVD-R, DVD+R) media have an organic dye layer that is burned irreversibly. The change in reflectivity produced when lasering that dye layer against a reflective layer is a greater change than with phase-change alloys.
Both Recordable and ReWritable CD media are also hampered by a very thin top protective layer. Microwave a coastered CD-R for a few seconds till it flashes and flakes, and see just how thin and fragile this layer is.
DVD-R/RW media is much more robust - the recordable layer is sandwiched in between two plastic layers, so I'd expect the lifespan of recorded DVDs - even based on the exact same dye - to be considerably longer than recorded CDs.
The question of whether Recordable or ReWritable media has a longer life span is one I haven't seen explored very well at all (though, and I think this was your main point), glass-mastered/stamped CD- and DVD-ROM media certainly do last longer than either.
One odd but explicable trend in Recordable media aging is that the shelf-life of a dics once written is longer than that of a blank disc. Don't get too enthused about stocking up on cheap CD-Rs or DVD-/+Rs at a sale - if you leave them sitting on a shelf too long before burning them, they will go unreliable.