Data lakes and data warehouses used to be completely different animals, but now they seem to be merging. A data lake was a single data repository that held all your data for analysis. The data was stored in its native form, at least initially. A data warehouse was an analytic database, usually relational, created from two or more data sources. The data warehouse was typically used to store historical data, most often using a star schema or at least a large set of indexes to support queries.