Balancer is a utility provided by HDFS. As we know that, DataNodes stores the actual data related to any job or process. Datasets are divided into blocks and these blocks are stored across the DataNodes in Hadoop cluster. Some of these nodes are underutilized and some are overutilized by the storage of blocks, so a balance needs to be maintained.   Here comes the use of balancer which analyses the block placement across various nodes and moves blocks from overutilized to underutilized nodes in order to maintain balance of data across the DataNodes until the cluster is deemed to be balanced.