I'm looking for a way to prove that a certain amount of data was stored, through some easily verifiable piece of information. Similarly to how proof-of-work can prove through a hash that a certain amount of work was done to generate such hash.

I don't need this "proof" to tell me whether that data is currently stored somewhere, I'm just interested in proving that a certain amount of data was stored (anytime in the past) via some sort of hash or other piece of information.

For instance, imagine I have to prove to someone that I was able to store 5 GB. Doesn't matter where, I could use many different computers. One requirement I guess is that the proof should be easy to validate.

Any ideas?