Mostly how much data there is, and how structured it is. Not really sure what the difference between data lake and warehouse is, but either of them will typical

Mostly how much data there is, and how structured it is. Not really sure what the difference between data lake and warehouse is, but either of them will typically have less structured data and more of it than an SQL server. We're talking petabyte-scale. Sure, you can get 16TB drives, but it's still a stretch to put it all on a single machine. Data should ideally be stored as parquet or similar, but there's probably a lot of JSON out there. Couple it with something like Athena, and you can query in SQL. Spark for more complicated stuff.