CDR/DVDR decay?

Hi /tech/

You know how old tapes used to become shitty after a certain amount of time? Well, maybe not since noone uses tapes anymore, but they do. I dunno how it works, the magnetic signal fades or whatever.

Anyway, my question is; does something similar happen to CDs and DVDs? And in particular the recordable/rewritable versions? If I store stuff on CD or DVD today, and I let it sit unused in a box somewhere in the attic (safe from moisture and dust, maybe not 100% safe from temperature but mostly anyway), will it remain 100% intact over the years, or will the things degrade over time?

If they do decay, how long does it take for the date stored on it to get corrupted? And what would be the safest way to store digital data for very long periods if CDs/DVDs aren't 100% safe?

Maybe it's a stupid question, but I really don't know anything about how these things work, and I really want to know.

CDs do decay over time, recordables in particular and rewritables probably even more so. Sun light is very bad for such media, as well as moisture. If you want to keep Data on such media for a very long time, you should shut them away in a safe somewhere. I doubt you can keep favorable conditions in your attic. Also, there is probably a reason why lots and lots of people are still using magnetic tapes for long term backups.

I'm not an expert on this subject, so I won't go any deeper. But the essence is: CD/DVD media do decay over time. How fast depends on the type of media and the conditions, but they do.

Longevity varies from 2 months to 10+ years depending on manufacturer. At the high end, there are professional archive discs for recording studios and such for about $15/disc. Mitsui and Kodak used to make those, I think.

The laser burns a layer of dye, and that dye can rehomogenize and lose the burn pattern if formulated badly like the cheap Chinese manufacturers do. I think CMC was the WORST manufacturer.

Any disc you burn has errors. The software recovers from the errors using parity values, or extra bits. Use a program like KProbe2 to count the errors and watch your disc decay over the months.

ALTERNATIVES
Tapes are the most common alternative. Rated 10 to 30 years, and large enough to backup a server. I suppose an external hard drive is the equivalent for the home user.

There are already holographic storage devices on the market, but they're $10,000 and meant for big companies. Hopefully that will get cheaper and replace dye-based discs.

Personally, I copy my MOST important documents/pictures to a bit pattern that I print on archival quality paper with one of those Epson inks rated for UV exposure and guaranteed for years. I can scan the bit pattern back in from paper if my DVD copy fails.

Others have done something similar with 35mm film since it is very stable for 100+ years.

DON'T LISTEN TO HIM!! ^{HE'S FROM ALABAMA!!}

Is >>4 an EXPERT PROGRAMMER!!!?

Burned discs contain organic material (rip one apart and rub it on your hand sometime to see) and will start to ruin on the outter edge first since that is where they are the weakest. That is why if you plan to use a disc for long-term storage, you should only use it to 60% capacity. Optionally use the remaining area of the disc for storing ECC data.