A petabyte. That’s a thousand terabytes. From The Conversation:
In Nature Communications today, we [Min Gu et al] along with Richard Evans from CSIRO, show how we developed a new technique to enable the data capacity of a single DVD to increase from 4.7 gigabytes up to one petabyte (1,000 terabytes). This is equivalent of 10.6 years of compressed high-definition video or 50,000 full high-definition movies.
The technique is basically two concentric beams of light — one writes the tiny dot that represents a single bit, and the other interferes with the first one, which effectively narrows the beam. Thus you can get more dots in the same amount of space.
Obviously products are some years in the future still.