From online training firm Edureka Question and Answers
Map Reduce: http://www.edureka.co/blog/hadoop-interview-questions-mapreduce/
Hadoop Cluster: http://www.edureka.co/blog/hadoop-interview-questions-hadoop-cluster/
HDFS: http://www.edureka.co/blog/hadoop-interview-questions-hdfs-2/
PIG: http://www.edureka.co/blog/hadoop-interview-questions-pig/