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Old October 18th, 2007, 02:56 PM   #1
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using optical media for long-term data storage

Here are some thoughts on long-term storage. I haven't found an existing tread, so I started a new one. I wanted to reuse my tapes, so choosing proper optical format was essential. I researched this matter and here is what I found.

All optical disks:
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* susceptible to scratches on read side

Pressed disks (CDs and DVDs):
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* Have stable quality
* Do not "fade" provided that they are properly manufactured
* Not susceptible to UV light
* Not susceptible to scratches on label side

CD-R:
-----

* Susceptible to UV light, don't leave disks "silver" side up for the long time
* Susceptible to scratches on label side, because the label is actually a reflective foil glued to the disk.

DVD -R, +R, RW:
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* susceptible to UV light
* Not-susceptible to scratches on label side, because the reflective layer is enclosed inside the disk. Yeah, baby!

DVD-R:
------

* Better error-correction scheme than recordable CDs

DVD+R:
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* Better error-correction scheme than DVD-R
* Originally less compatible with older equipment like DVD players
* Assignable book type improves compatibility with DVD players and computer drives

RW disks (CD and DVD):
----------------------

* Not intended for long-term storage, data can "fade" over time
* Disk can become unwritable over time

Double-layer DVDs:
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* Require higher quality components and stricter production control

The bottom line:
----------------

I don't think that anyone on this forum would consider using recordable CDs because they hold only 700MB. I decided for myself that DVD+R is the way to go even for smaller files. My computer drive and my DVD player read these disks with no problems. Pressed disks are the best if you can afford it and your production is really worth preserving.

When buying disks choose carefully, quality differs from manufacturer to manufacturer and also depends on dye type. Some dyes deteriorate faster and are more susceptible to UV light that others. Choosing by dye color is not safe because manufacturers add coloring to the dye.
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Old October 18th, 2007, 06:51 PM   #2
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I personally only use Taiyo Yuden DVD-Rs or Verbatim DVD+R's. Both are among the highest-quality media for duplicated DVD's.

Verbatim DVD+R DL are also great for dual-layer content.

Blu-Ray (not sure on HD-DVD) is proclaimed to have a 100 year life-span, but I don't have any hard data on that. It will be interesting when the next-gen burners and media start becoming more affordable.

Check out www.cdfreaks.com for more information on the best quality media to use and to find where on the scale your current media lands.
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Old October 18th, 2007, 08:22 PM   #3
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DVD-R manufacturers also claim 100 years life span, but in reality, only 10 years average. Even a MiniDV can outlast any optical storage.
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Old October 18th, 2007, 09:12 PM   #4
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MiniDV can get dusty, though, etc... not exactly easy to clean.

I suggest two copies of anything on CD or DVD.

When one gets too old, backup the other. (ie keep a "using" disc and a "saving" disc)

Works great.
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Old October 18th, 2007, 09:25 PM   #5
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Also be caredul about storage temperature for CD/DVD as it can really shorten the data retention period.

Tape has by far the best proven archival life of any rewritable media (except maybe paper and stone tablebs!)

There was an industy report released in Japan in March where they tried to asses the permanence of various brands and types of media. The good news was that in many cases one could expect 10 to 30 years of life based on accelerated stress testing.

The less good news was that some types/brands showed extremely long lifetimes at room tem@eratures, but very very poor results at any kind of elevated temperature.

The really bad news was that around 40% of all the samples submitted by the various manufacturers failed to pass the minimum level of testing needed to even be included in the longer term study.
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Old October 18th, 2007, 09:30 PM   #6
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Jim, what format and what brands did that study include...?
ie, "various types" that all last "10 to 30 years" is a bit vague....
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Old October 18th, 2007, 10:30 PM   #7
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Yes, I know it's a bit vague, but that's partly because the gentleman who sent me the info only summarized it because he wasn't sure the document itself was OK for public distribution.

I had asked him about this a couple of months ago and he had told me about what I relayed.

However, he said that it was a study of all brands and types manufactured by the Japanese companies, and that there was no particular correlation between brands or media types and longevity or failure.

The way I think it should be interpreted is that the jury is still very much out on the subject of archival permanence, and everything that is published is still based on stress studies, as nobody has yet tried to store a DVD for 100 years. And there isn't really a definitive study that everybody salutes.

Tape, on the other hand, has been around for 50 to 60 years and there is a lot of hard experience about it's longevity. The petroleum companies have hundreds of millions of cartridges that have been around for decades and are still usable.

If it were my data, I would probably opt to store it on optical as well as keep the original tapes, and keep everything in an air conditioned environment and check the media every few years as well - if not just re-copy on a regular basis. Maybe I'm paranoid, though!
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