gddrescue is more universal.

But both tools are just limited by hardware restrictions.

If a CD's sector is unreadable, the drive usually refuses to let the computer know about the subcode.

For damaged discs, could dvdisaster actually be more suitable or equally suitable as gddrescue?

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    Even the gddrescue can be used for optical media, too, the dvdisaster may use CD/DVD specific tricks to peek out the data relict from scratchfull disc. The main diference between magnetic and optical record is re-coding of the data (one part of mastering process). In the Yellow book you can find more details about the data recoding and data protect features used on optical media. (Form 1 of CD-ROM XA had more than 256 bytes "CRC" for each 2048 bytes sector) – schweik Oct 19 '18 at 7:29

gddrescue seems to be a replica that tries to reimplement the features from sdd, but since sdd is not useful for optical media, the same applies to gddrescue.

The reason is that if you access optical media at UNIX driver level, you rely on the error recovery features of the driver from the OS. This driver is not written for optical media but for hard disks and id usually much worse than what you may get from software that was designe for optical media.

I recommend to use readcd -noerror from the cdrtools, it directly accesses the drive using own SCSI commands send via the SCSI generic interface. Recent versions are in the schilytools source tree. Readcd even includes a reed solomon decoder that may help in case that the error recovery in the firmware of a CD drive is not optimal. The reed solomon decoder is activated by the option -edc-corr option.

Note that the strength of the error recovery is controlled by the retries= option.

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