Optical media (CD,DVD,BD) keep their data only for a finite time (typically for many years). After that time, data loss develops slowly with read errors growing from the outer media region towards the inside.
You can check a mirror of the official website here:
Or this one (no images):
https://cdn.rawgit.com/lrq3000/dvdisaster/stable/dvdisaster/documentation/en/index.html
Archival with data loss protection
dvdisaster stores data on CD/DVD/BD (supported media) in a way that it is fully recoverable even after some read errors have developed. This enables you to rescue the complete data to a new medium.
Data loss is prevented by using error correcting codes. Error correction data is either added to the medium or kept in separate error correction files. dvdisaster works at the image level so that the recovery does not depend on the file system of the medium. The maximum error correction capacity is user-selectable.
Common misunderstandings about dvdisaster:
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dvdisaster can not make defective media readable again. Contents of a defective medium can not be recovered without the error correction data.
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Such functions are outside the scope of dvdisaster's internal design and goals.
