“big data” is when the size of the data itself becomes part of the problem.
Note: definition of bigdata
Information platforms are similar to traditional data warehouses, but different. They expose rich APIs, and are designed for exploring and understanding the data rather than for traditional analysis and reporting. They accept all data formats, including the most messy, and their schemas evolve as the understanding of the data changes.
Managing sharding and replication across a horde of database servers is difficult and slow.
The need to define a schema in advance conflicts with reality of multiple, unstructured data sources, in which you may not know what’s important until after you’ve analyzed the data.