What does rack awareness mean?

In a large cluster of Hadoop, keeping in mind the end goal to enhance the network traffic while perusing/composing HDFS file, name-node picks the data node which is nearer to a similar rack or close-by rack to Read/Write ask. Name node accomplishes rack data by keeping up the rack id’s of each data node. This idea that picks nearer data nodes, which are based on rack data is called Rack Awareness in Hadoop. Rack awareness consists of the knowledge of Cluster topology or more specifically how the different information nodes are conveyed over the racks of a Hadoop cluster. Default Hadoop installation expects that all data nodes belong to with a similar rack.