Hi Geoffrey - thanks for your suggestions but it wasn't the cause of my issue. I fixed my issue by doing the following: for i in {1..12} ; do echo $i cd /grid/$i/hadoop/hdfs/data rm -rf current done My problem was that the 12 drives in the DataNode must have had old hdfs data so I deleted it with above script. After that everything worked ok! So lesson learned is that I will ensure the /grid structure is clean before adding any nodes! Thanks! ... View more