I want to deploy a small data center for data analysis purposes. I will get the data mostly from web applications. I know I can setup a hadoop cluster and scale it as per necessity. I also know that OpenStack is a free and open-source software platform for cloud computing, mostly deployed as an infrastructure-as-a-service (IaaS). However, it is apparent that some industries are preferring hadoop on top of OpenStack (Sahara). Thus, I want to know the difference, advantage and disadvantages of Hadoop features with or without OpenStack.

In brief, if I put Hadoop on top of OpenStack, what extra features do I get?