"What is DISADVANTAGE about Rack Awareness at this point is the manual work required to define it the first time, continually update it, and keep the informatio

"What is DISADVANTAGE about Rack Awareness at this point is the manual work required to define it the first time, continually update it, and keep the information accurate. If the rack switch could auto-magically provide the Name Node with the list of Data Nodes it has, that would be great." This is where LLDP comes in handy. Run an LLDP agent on each node and enable LLDP on the switch access ports. Then it's just a matter of the NameNode fetching LLDP neighbor information from the switch (usually by using SNMP) and updating it's Rack Awareness. (Disclaimer: I know nothing about Hadoop...)