@Manish thakur If we decommissioned a datanode, then namenode will look for the blocks from that decommissioned datanode. If Namenode not receiving any update from that datanode, then namenode mark that datanode as dead datanode after 10m. 30sec and replicate the under replicated blocks to another datanode as per rep. factor 3. So the decommission will not effect the data available in the datanode. ... View more