Scenario when the name node and data node is down in Hadoop  cluster

1- While configuring the hdfs makes ure the proper directory has to be added in to the hdfs-site.xml else it will create default directory structure in  the below directory file://tmp/dfs/name so if accidentaly delete the content of temp file from the server then the name node and data node will not up.

2- If any of the  cases where  HDFS abruptly shutdown then  the data node  heart-beat /state wont sync up with the name node heart beat,So even NN up the data node(DN) wont up

Ans:- Hence  in that case    :dfs/data/current/Version  state number should not be sync with the Version exist in the :dfs/name/Current /Version so in that case stop all the service by stop-all.sh
and the  sync  both the state  and  start-all.sh   .