you can comfortably fit 8TB of data on a single box running postgres, more dependent on your hardware :)
Of course, that's in a Spark cluster running massively parallel queries and not on a single (however large) node.
That’s no criticism at all. I wouldn’t use Spark for a transactional DB because it’s not the best tool for the job. Same for PostgreSQL when the dataset grows far beyond what a single instance can reasonably process.