Life and Death of Storage Devices 1: CD-R/DVD-R Discs

In Tanzania we are using 3 different kinds of hardware to store and share our data: CD-Rs/DVD-Rs discs, Flash drives, and (mechanical) hard disks. TZ is a harsh environment for each of these kinds of storage. I am sure you have seen each of them fail. The interesting thing is that each of them stop working in a different way. In this post I will describe the failure mode of each kind of device, as I understand them.

Dye on old CD-R is starting to dissolve, Via Wikipedia

CD-R/DVD-R:

CD-R and DVD-R are based on a similar idea. There is a layer of the disc which is reflective like a mirror. There is at least one other layer which has some special ink frozen in plastic and one more extra layer of plastic to try to protect the ink. The red laser inside the DVD or CD reader tries to change the ink or dye in millions of places/dots so that it can store data.

The most common way CD/DVD fail is by becoming scratched. As those of us that piga deki every couple days know, Africa is quite a dusty place–that dust scrapes at the plastic very easily leaving places where the laser is trying to read. Another possible way to damage a dvd is by breaking it so the ink spills a little or the reflective layer doesn’t reflect the laser back to the DVD player eye.

Perhaps the most interesting failure of CD/DVD is when a certain bacteria eats away at the reflective layer. Also if you buy certain  DVD-R/CD-R the ink formula may be low quality and might not hold the dots “color” very well. As the “color” changes around the disc the data is slowly lost. If you leave a CD-R in the sun you might also notice data loss. There are more details on the Wikipedia page for CD-R.

For a larger hardware problem, with the dirt in the air, the mechanics of the CD-ROM drive often seem to fail so that the door to the drive does not open reliably. I have read some accounts that it is because the rubber band/string is getting stretched and so the drive doesn’t recognise that the eject button is pressed as easily. According to websites, you can replace the band and it will often start to eject properly again but we haven’t tried it at our college.