What are the main causes of optical media corruption?

Question

I burned an Ubuntu 10.04 ISO to a CD-R (using the slowest speed there was in the software) only little over a month ago. I just checked the md5 now and found out that the disc had become corrupt. The disc hadn't been exposed to sunlight, or kept in a humid place, or been hit or dropped. I had only used it once for installation and that was it - put it in its case and kept it "safe" (or so I had thought). And the disc wasn't really the cheapest either. So what is it that could/does cause corruption to CD's within such short time?

Answer 1

The problem is material degradation. Optical discs commonly used for burning, such as CD-R and CD-RW, have a recording surface consisting of a layer of dye that can be modified by heat to store data. The degradation process can result in the data "shifting" on the surface and thus becoming unreadable to the laser beam.

"Many of the cheap burnable CDs available at discount stores have a life span of around two years," Gerecke says. "Some of the better-quality discs offer a longer life span, of a maximum of five years."

-- From PCW

The lifetime of many articles follows a bell-curve, so if the average is 2 years, in a large enough sample you'll find one that lasts a month.