So, turns out Mirror is a nice frontend capable to write onto two blockchains: Ethereum and Arweave. The first one is used as permanent registrar of the event (i.e.: a new post is published), the latter instead is the content storage infrastracture. The media or this text itself will be written on the Arweave blockchain. I have to admin I did not know Arweave. I will have to study a little bit more how it works and how it is going to maintain the transactions costs as little as they are right...