Even with ddrescue you might lose a few bits. You will only find out when accessing those specific files and bits.
For my photo history I prefer to keep PAR files next to it. On a running mechanical disc I haven't seen issues when running the repair. I do expect to see some errors in the future and as long as it stays under a certain percentage, things will be fixable.
I started doing this long time in the past, when harddisks were awful. I would often lose mp3 files due to damage. With mp3 you can easily hear it. With jpeg images you can often see damage as well.
If you pay attention to the ddrescue output it is pretty obvious when you are missing a few bytes here and there.
I have long since moved away from optical media, really for anything, but especially archival. Long term storage to me looks like an array of magnetic disks held together with ZFS.
Not much point, way too time consuming. I dumped hundreds of CDs/DVDs as most of them were unreadable. 20% of them might still good, but really no longer had that energy to savage them.
PAR files are a form of Forward Error Correction (FEC) (implemented with Reed Solomon). They can be used to repair some percentage of damaged blocks in a file or set of files. The percentage is determined ahead of time when you generate the FEC (PAR files) and imposes the same amount of storage overhead (i.e., 15% redundancy costs 15% additional disk space with Reed-Solomon).
For my photo history I prefer to keep PAR files next to it. On a running mechanical disc I haven't seen issues when running the repair. I do expect to see some errors in the future and as long as it stays under a certain percentage, things will be fixable.
I started doing this long time in the past, when harddisks were awful. I would often lose mp3 files due to damage. With mp3 you can easily hear it. With jpeg images you can often see damage as well.