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."

Comments

dvdisaster

[Anonymous Coward]

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

Re:dvdisaster

[MarkGriz]

Great idea!

For a less technological approach, I simply BUY whatever CD or DVD I want to keep.

I thought about doing that, but wasn't able to find any of my source code or family photos on DVD at my local store. Maybe I'm just looking in the wrong place. Where do you shop for yours?

I highly recommend using Archival Grade Media

[Phizzle]

Archival Grade Media makes a HUGE difference for backing up important data. It is not very expensive and widely available.

Re:I highly recommend using Archival Grade Media

[Yewbert]

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.

Error-Proofing Data With Reed-Solomon Codes

[MarkoNo5]

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

Professional Advice

[polyomninym]

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!

Re:The tools are called

[digitalchinky]

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.

Mod parent up!

[GroundBounce]

I have many gigs of digital photos and I have also more-or-less moved away from optical media for backup and switched to HDD. As the original poster mentioned, most of the "information" you find on the net about archival longevity of optical media is personal anecdotes or pet theories, and good hard data on archival longevity of CD-R or DVD+-R is hard to find. My own personal experience is that name brand discs do have fewer problems than cheap "house brands", but it's hard to quantify or say much beyond that.

Backing up to hard drives has a number of advantages:

1. It's a heck of a lot easier - in most cases of personal data backup, a few 1TB HDDs will hold all the data you need to back up, so there's no need to manage boxes of 100's of discs. I usually back up the same data onto two HDDs, and store one of them in a firesafe. If you're really worried, you can store one of them offsite.

2. Since no media will last forever, you will *always* need to roll your data over to new media every so many years. With HDDs, its *much* easier to roll your data over to new media every 5 or 6 years. Think of transferring two or three HDD's to a new HDD (by the time you roll over the data, the new HDD will probably hold all the data from those two or three older HDDs), compared to re-organizing and re-burning hundreds (or more) of CDs or DVDs.

The bottom line is that if a few HDDs don't hold enough data for your needs, then backing up to optical media will be totally out of the question anyway, and you will probably need to use tape.

Titanium Plates © if your data matters

[Phizzle]

Take a page from the book of Church© of© Scientology©®(TM) and engrave your data on Titanium© Plates© and store it in Gold© Vault©. I apologize in advance to the Church© of© Scientology©®(TM) if I didnt use enough Copyright©®(TM) symbols while referring to Them (©?). Please do not sue me. © (TM) ®