Comment by adrian_b

When only a number of 4 kB blocks cannot be read, if the amount of affected data is less than the amount of added redundancy the archive file can still be repaired.

For instance, if you have a 40 GB backup archive with 10% redundancy, 4 GB of data, i.e. one million 4 kB data blocks can be unreadable and you can still repair the archive and recover the complete content.

It is true that the entire SSD or HDD can become bricked. The solution for this, as I have already written in my previous comment, is to duplicate any SSD/HDD used for archival purposes, which I always do.