Hi PA, We just did the same work recently, copying data from hadoop 2 to hadoop 3, to be precise, src hadoop version was CDH hadoop-2.6 (5 hdfs nameservices federation), dst hadoop version was hadoop 3.3.4. Both clusters are protected with Kerberos, and of course, two realms have been trusted with each other. We executed the DistCP on hadoop 3 version cluster, but also tried on hadoop 2. Both were working nicely. I can confirm that copying data with DistCP from 1.x to 2.x needs webhdfs, which is slow compared to rpc one. Here is an execution example:
hadoop --config /home/hadoop/conf distcp \ -Dmapreduce.job.hdfs-servers.token-renewal.exclude=ns1,ns2,ns3,ns4,ns5 \ -update -skipcrccheck \ hdfs://hadoop2-cluster/user/test \ hdfs://hadoop3-cluster/user/test
