Question - What is rack awareness in Hadoop clusters?
Answer -
Rack awareness is one of the mechanisms used by Hadoop to optimize data access when processing client read and write requests. When a request comes in, the NameNode identifies and selects the nearest DataNodes, preferably those on the same rack or on nearby racks. Rack awareness can help improve performance and reliability, while reducing network traffic. Rack awareness can also play a role in fault tolerance. For example, the NameNode might place data block replicas on separate racks to help ensure availability in case a network switch fails or a rack becomes unavailable for other reasons.