The disc is easy to lose data if taking physical damages.
If the disc is a store with data files independently, just copy the files to the hard disk to back up the data.
However, if the disc is an install disc, although the files are copied, some of them cannot be functioned.
If back up a disc with an ISO file, we can write a disc on any time with any disc writer.
Insert and load the disc
Open Terminal and type
ls -l /dev/*rom
Check out which CD/DVD ROM is using
dd if=/dev/<your CD/DVD ROM> of=<output file>
if the path of if or of including space(s), the string of path must use ‘ or “