There is "dfs.hosts.exclude" configured before NN start. Active/Standby works well.
1)Add two datanodes IPAddr to the exclude file on the both Active and Standby NN.
2)run: hdfs dfsadmin -refreshNodes on the Active NN, but there isn't any logs in the ActiveNN log. but decommission logs showed in the StandbyNN log.
There is no decommission datanodes showed on the Active NN webUI. but there does have decommission datanodes showed on the Standby NN webUI.
But the decommission process is very very slow, it indicates it cannot finish forever.
I do think this is a bug.