On Wed, 2022-11-09 at 14:22 +0100, Nicolas George wrote: > hw (12022-11-08): > > When I want to have 2 (or more) generations of backups, do I actually want > > deduplication? It leaves me with only one actual copy of the data which > > seems > > to defeat the idea of having multiple generations of backups at least to > > some > > extent. > > The idea of having multiple generations of backups is not to have the > data physically present in multiple places, this is the role of RAID. > > The idea if having multiple generations of backups is that if you > accidentally overwrite half your almost-completed novel with lines of > ALL WORK AND NO PLAY MAKES JACK A DULL BOY and the backup tool runs > before you notice it, you still have the precious data in the previous > generation.
Nicely put :) Let me rephrase a little: How likely is it that a storage volume (not the underlying media, like discs in a RAID array) would become unreadble in only some places so that it could be an advantage to have multiple copies of the same data on the volume? It's like I can't help unconsciously thinking that it's an advantage to have several multple copies on a volume for any other reason than not to overwrite the almost complete novel. At the same time, I find it difficult to imagine how a volume could get damaged only in some places, and I don't see other reasons than that. Ok, another reason to keep multiple full copies on a volume is making things simple, easy and thus perhaps more reliable than more complicated solutions. At least that's an intention. But it costs a lot of disk space.