If you want to understand big data, you need to understand Hadoop. Hadoop is the technology underlying many big data efforts. But most of the descriptions of Hadoop are jargon laden and impenetrable to newcomers. Well, maybe just impenetrable to this newcomer. But one great revelation to me was a historical note as to WHY there was a need to develop Hadoop. It was all those pages that had to be indexed by search engines at Google and Yahoo. So I went out to try to find more details. This article, with a ton of references throughout, is an excellent introduction to the precursors to Hadoop, the development of Hadoop itself, and the explosion of systems that used Hadoop as their foundation.
Marko Bonaci. The history of Hadoop. Medium, April 11, 2015. Available at https://medium.com/@markobonaci/the-history-of-hadoop-68984a11704.