Always look to nature first. Nature never lies. DNA storage:

Escherichia coli, for instance, has a storage density of about 10 to the 19 bits per cubic centimeter. At that density, all the world’s current storage needs for a year could be well met by a cube of DNA measuring about one meter on a side.

There are several companies doing it: https://www.scientificamerican.com/article/dna-data-storage-...