I presume DVD is reasonably safe as long as the discs are of good quality, they are burned with a good quality recorder at their rated speed and they are stored carefully (cool dark place away from extremes of humidity or chemical fumes) and handled carefully (no fingerprints on recording surface, no abrasive or solvent cleaners used, no bending/dropping/etc.). Some high-quality CDs claim 100 years under optimal conditions.
However, media quality is very important - I've got some data on CD-Rs which I have used regularly and still have no problems with. The discs were burned in early 1998 - so are over 6 years old. However, they are definitely high quality discs using 'archive' grade dye and pure gold for the metallic layer, and I have stored them very carefully.
Conversely, I have used some cheap no-name discs for in-car use. In-car storage is very harsh - extremes of temperature, humidity and exposure to sunlight. The worst batch of discs I got lasted less than 2 weeks before they were wrecked. The dye 'faded' where sunlight had penetrated the label layer and the metal layer peeled off.
If you use DVD backup, then with care it can be quite reliable (good quality discs and careful storage are absolutely required). Some manufacturers have performed 'simulated aging' on their discs (e.g. baking them in ovens at high humidity) and have calculated useful lifetimes of over 100 years. However, I don't know of any studies that have looked at other types of failure (e.g. long-term exposure to low-intensity sunlight, whether a finger print on the optical surface could corrode the plastic over years, whether solvents from spray polishes or ozone emissions from laser printers affect the discs).
Whenever you backup to any media, I would always recommend verifying that the data was written correctly, particularly with optical media like CD or DVD. There is always a small chance of a manufacturing flaw in the disc or a dust particle causing part of the recording to be of low quality, and possibly unreadable. (I remember the with same ultra-cheap CD-Rs as above a couple actually had air bubbles in the plastic substrate - they didn't burn very well).
However, media quality is very important - I've got some data on CD-Rs which I have used regularly and still have no problems with. The discs were burned in early 1998 - so are over 6 years old. However, they are definitely high quality discs using 'archive' grade dye and pure gold for the metallic layer, and I have stored them very carefully.
Conversely, I have used some cheap no-name discs for in-car use. In-car storage is very harsh - extremes of temperature, humidity and exposure to sunlight. The worst batch of discs I got lasted less than 2 weeks before they were wrecked. The dye 'faded' where sunlight had penetrated the label layer and the metal layer peeled off.
If you use DVD backup, then with care it can be quite reliable (good quality discs and careful storage are absolutely required). Some manufacturers have performed 'simulated aging' on their discs (e.g. baking them in ovens at high humidity) and have calculated useful lifetimes of over 100 years. However, I don't know of any studies that have looked at other types of failure (e.g. long-term exposure to low-intensity sunlight, whether a finger print on the optical surface could corrode the plastic over years, whether solvents from spray polishes or ozone emissions from laser printers affect the discs).
Whenever you backup to any media, I would always recommend verifying that the data was written correctly, particularly with optical media like CD or DVD. There is always a small chance of a manufacturing flaw in the disc or a dust particle causing part of the recording to be of low quality, and possibly unreadable. (I remember the with same ultra-cheap CD-Rs as above a couple actually had air bubbles in the plastic substrate - they didn't burn very well).
