问题：
2019-05-05 11:36:41,610 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for block pool Block pool BP-786145861-192.168.56.101-1557024630493 (storage id DS-755323433-192.168.56.102-50010-1557025295787) service to h1/192.168.56.101:9000
org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.server.protocol.DisallowedDatanodeException): Datanode denied communication with namenode: DatanodeRegistration(0.0.0.0, storageID=DS-755323433-192.168.56.102-50010-1557025295787, infoPort=50075, ipcPort=50020, storageInfo=lv=-47;cid=CID-6a141ff8-2747-4a4a-9529-96f5804fdacf;nsid=1045560575;c=0)
2019-05-05 11:36:41,617 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool BP-786145861-192.168.56.101-1557024630493 (storage id DS-755323433-192.168.56.102-50010-1557025295787) service to h1/192.168.56.101:9000
解决方法：
Essentially , the reverse DNS lookup needs to be set up to solve this issue if the cluster is using a DNS Resolver then this needs to be set up at the DNS server level or if the Name Nodes are looking into /etc/hosts file to find Data Nodes then there needs to be any entry for the Data nodes there.