In HDFS, how Name node determines which data node to write on?

[#1]

How Name node determines which data node to write on in HDFS ?

[#2]

Namenode contains Metadata i.e. number of blocks, replicas, their location, and other details. This meta-data is available in memory in the master for faster retrieval of data. NameNode maintains and manages the Datanodes, and assigns tasks to them.