Datanode is a daemon in architecture and there are multiple instances of datanodes depending upon the size of the cluster and these are slaves of hadoop architecture, and data nodes report to Namenode. Data nodes stores the data. Datanodes are the slaves which are deployed on each machine and provide the actual storage. These are responsible for serving read and write requests for the clients.
There are a Number of datanodes, usually one per node in the cluster, which manage storage attached to the nodes. Internally , a file is split into one or more blocks and these blocks are stored in a set of datanodes. The Datanodes are responsible for serving read and write requests from the file system's clients