Storage densities can be extremely high. Filling 2^64 of storage is very doable and people have been doing it for a while. It all moves downstream; I remember when a 2^32 was an unimaginable amount of storage.

Many petabytes fit in a single rack and many data sources generate several petabytes per day. I'm aware of sources that in aggregate store exabytes per day. Most of which gets promptly deleted because platforms that can efficiently analyze data at that scale are severely lacking.

I've never heard of anyone actually storing zettabytes but it isn't beyond the realm of possibility in the not too distant future.