It’s technically illegal to make a copy of that data for yourself and then to sell the original (while keeping the copy). That obviously doesn’t mean it doesn’t happen, but…
It’s not that straightforward. Copyright is different in that infringement is only enforced by rightsholders through litigation. That means they hato find you, sue you, and make a convincing argument that your backup is harming their market viability.
On that last point, some personal backup is unlikely to be found to be infringing. It’s more problematic if it’s something shared or done in a significant scale.
What about physical media containing digital data, e.g. a CD?
It’s technically illegal to make a copy of that data for yourself and then to sell the original (while keeping the copy). That obviously doesn’t mean it doesn’t happen, but…
It’s not that straightforward. Copyright is different in that infringement is only enforced by rightsholders through litigation. That means they hato find you, sue you, and make a convincing argument that your backup is harming their market viability.
On that last point, some personal backup is unlikely to be found to be infringing. It’s more problematic if it’s something shared or done in a significant scale.