Note: the 13 EiB pledged are real storage capacity: miners must provide a cryptographic proof every day, that they are storing this much space; or it doesn't count. I still think crypto valuations are excessively, tulip-y high, but valuation/byte is pretty similar.

The cryptographic system that enables people to prove storage is called 'Proof of spacetime'; which sounds cringey, but it's pretty clever (begins at page 10): https://filecoin.io/filecoin.pdf

Note that if you went to Backblaze and wanted to store 2 EB, it's unlikely they'll be able to serve you immediately (they probably can't get enough HDDs from their channels that quickly). However, you CAN store 2 EB on Filecoin the same way you can auto-scale on AWS.