After the Africa Special it was announced that DIDs and academic records of 5 million+ people will now be stored in the Cardano blockchain and this is set up to scale for massive adoption. Thus it raised the doubt: where does all of that information will be stored, in addition to cryto-transactions and the whole ecosystem that will be built? I mean in contrast to centralised institutions that own big computer clusters for the equivalent purpose, Cardano nodes can run on regular PCs, so how is it possible??
You don't have to store a lot of information on the blockchain itself to provide certain evidence. (that something existed at a certain time or was signed by someone, or that something was not tampered with).
Usually, it is enough to store for example a link to something and a hash or a signature. (i.e. onchain should be stored only the data that are absolutely necessary to prove the required evidence)
Metadata Example: please look into this transaction (on adastat go to metadata tab and look at the data that is actually stored onchain)
You will find the link to http://api.cardano.scantrust.io/publicdata/71a7f9d0.json (where the actual data is offchain, basically, this could even be stored somewhere where only a limited group has access to it)
A good onchain/offchain design combined with batch processing, therefore, enables the cost-effective use of blockchain technology and the preservation of privacy. (which is not Cardano specific)
To get an idea for example with Atala PRISM hundreds of credentials can be signed in only 1 (one) transaction.