Thanks for the suggestions.

I do have backups on optical media. Note that DVDs are assumed to be much less reliable than disks, and are much less convinent for use anyway.

In the past 10 years this happened several times and so it hints that the drives are not that great. Making multiple copies is good, but would require a manual merging phase in case things go wrong. This is where a straightforward Perl script can come in handy.

BTW, if you back up to optical media, have a look at DVDisaster. They give a good background and a nice program which I have been using for my backups.