Does NameNode provide with the IP address of data nodes where replication of data is to be stored

Question

In HDFS file write architecture, the client contacts the Name Node(NN). NN provides the IP address of Data Node(say Data Node. Does NN also provide with the IP address of data nodes where replication of data is to be stored OR  whether Data Node 1 (here) itself selects the other data nodes where replication is to be stored based on proximity(nearest Data Node)?

Answer 1

No, the data node does not select other data nodes where the replication is to be stored. The name node does that based on proximity. The importance of this knowledge relies on this assumption that collocated data nodes inside a specific rack will have more bandwidth and less latency whereas two data nodes in separate racks will have comparatively less bandwidth and higher latency.