First, some review

Hadoop is a very powerful MapReduce framework based on a white paper released by Google documenting how they have successfully tackled the issue of processing large amounts of data (on the scale of petabytes in many cases) using their proprietary distributed filesystem, GFS. Hadoop is the open source version of this distributed file system, heavily supported by companies like Yahoo, Google, Amazon, Adobe, Facebook, Hulu, IBM, RackSpace, etc. and has a growing number of related projects hosted by the Apache Foundation.