Full scan of 1 cubic mm of brain tissue took 1.4 PB – Google's AI experts assist (tomshardware.com)

Of course you don't need to store all the raw data though. Processing it and then throwing it away would allow you to churn through much larger parts of the breath this way without the absurd costs they calculate in this article.

Ongoing discussion https://news.ycombinator.com/item?id=40313193