Hadoop is similar in architecture to MPP data warehouses, but with some significant differences. Instead of rigidly defined by a parallel architecture, processors are loosely coupled across a Hadoop cluster and each can work on different data sources.
The data manipulation engine, data catalog, and storage engine can work independently of each other with Hadoop serving as a collection point. Also critical is that Hadoop can easily accommodate both structured and unstructured data.
This makes it an ideal environment for iterative inquiry. Instead of having to define analytics outputs according to narrow constructs defined by the schema, business users can experiment to find what queries matter to them most. Relevant data can then be extracted and loaded into a data warehouse for fast queries.
The Hadoop ecosystem starts from the same aim of wanting to collect together as much interesting data as possible from different systems, but approaches it in a radically better way. With this approach, you dump all data of interest into a big data store (usually HDFS – Hadoop Distributed File System). This is often in cloud storage – cloud storage is good for the task, because it’s cheap and flexible, and because it puts the data close to cheap cloud computing power.
You can still then do ETL and create a data warehouse using tools like Hive if you want, but more importantly you also still have all of the raw data available so you can also define new questions and do complex analyses over all of the raw historical data if you wish. The Hadoop toolset allows great flexibility and power of analysis, since it does big computation by splitting a task over large numbers of cheap commodity machines, letting you perform much more powerful, speculative, and rapid analyses than is possible in a traditional warehouse.