Hadoop has a master-slave architecture as shown in figure 1.1. A small Hadoop cluster consists of a single master and multiple worker nodes. The master node consists of a Job Tracker, Task Tracker, Name Node, and Data Node. A worker node acts as both a task tracker and a data node. A file on HDFS is split into multiple blocks and each block is replicated within the Hadoop cluster. [[File: Hadoop_1.png|thumb|upright=1|right|alt=Hadoop cluster|1.1 A multi-node Hadoop clusterCluster]]