From what I understand till now, the issues only appear on datanodes which are containing a large number of blocks and these datanodes contain far more blocks than the healthy ones. This can be remedied by running the HDFS Balancer.   In CDH 5.x, bug HDFS-6621 affects balancer performance. It is fixed in the GA releases 5.1.4 and 5.2.0 (and later versions like 5.3.0). It is not fixed in any 5.0.x version. So please consider upgrading to one of the above releases for the fix.   ... View more