Setting up multinode hadoop cluster Blockpool ID mismatch - hadoop

Question

While setting up multinode hadoop cluster I faced up several issues.
Going through different web portals for correct setup. Some fundamental question arose
I am using Hadoop 2.8.5 to set up a 2 node cluster in master slave configuration.
On first machine format the namenode using hdfs namenode format
clusterID and BlockpoolID got assigned like below:
#Fri Mar 29 11:14:41 IST 2019
namespaceID=576041649
clusterID=CID-98480e8d-f7a9-4e1a-8997-400a7aa150c3
cTime=1553838281164
storageType=NAME_NODE
blockpoolID=BP-954411427-x.x.x.y-1553838281164
layoutVersion=-63
Now on the 2nd machine, I ran command hdfs namenode format -clusterId CID-98480e8d-f7a9-4e1a-8997-400a7aa150c3
#Fri Mar 29 11:15:38 IST 2019
namespaceID=304822257
clusterID=CID-98480e8d-f7a9-4e1a-8997-400a7aa150c3
cTime=1553838338130
storageType=NAME_NODE
blockpoolID=BP-1421744029-x.x.x.x-1553838338130
layoutVersion=-63
Considering the slave and master should have same clusterID, Correct me if I am wrong.
The configuration seems to be working correctly but I am getting error in logs at logs/hadoop-cassandra-datanode-localnosql1.log and logs/hadoop-cassandra-datanode-localnosql2.log
2019-03-29 11:25:44,009 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool BP-954411427-x.x.x.y-1553838281164 (Datanode Uuid 4b90bebb-3c34-43d5-8285-6ec6dfefc0a7) service to localnosql1/x.x.x.x:8020 Blockpool ID mismatch: previously connected to Blockpool ID BP-954411427-x.x.x.y-1553838281164 but now connected to Blockpool ID BP-1421744029-x.x.x.x-1553838338130
2019-03-29 11:25:49,010 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool BP-954411427-x.x.x.y-1553838281164 (Datanode Uuid 4b90bebb-3c34-43d5-8285-6ec6dfefc0a7) service to localnosql1/x.x.x.x:8020 Blockpool ID mismatch: previously connected to Blockpool ID BP-954411427-x.x.x.y-1553838281164 but now connected to Blockpool ID BP-1421744029-x.x.x.x-1553838338130
2019-03-29 11:25:54,012 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool BP-954411427-x.x.x.y-1553838281164 (Datanode Uuid 4b90bebb-3c34-43d5-8285-6ec6dfefc0a7) service to localnosql1/x.x.x.x:8020 Blockpool ID mismatch: previously connected to Blockpool ID BP-954411427-x.x.x.y-1553838281164 but now connected to Blockpool ID BP-1421744029-x.x.x.x-1553838338130
2019-03-29 11:25:59,013 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool BP-954411427-x.x.x.y-1553838281164 (Datanode Uuid 4b90bebb-3c34-43d5-8285-6ec6dfefc0a7) service to localnosql1/x.x.x.x:8020 Blockpool ID mismatch: previously connected to Blockpool ID BP-954411427-x.x.x.y-1553838281164 but now connected to Blockpool ID BP-1421744029-x.x.x.x-1553838338130
2019-03-29 11:26:04,014 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool BP-954411427-x.x.x.y-1553838281164 (Datanode Uuid 4b90bebb-3c34-43d5-8285-6ec6dfefc0a7) service to localnosql1/x.x.x.x:8020 Blockpool ID mismatch: previously connected to Blockpool ID BP-954411427-x.x.x.y-1553838281164 but now connected to Blockpool ID BP-1421744029-x.x.x.x-1553838338130
What these error logs are suggesting?
Does the blockpool ID on the all master and slave nodes need to be same like clusterId, If yes how to do that?

Answer 1

Why are you trying to format namenode twice? Ideally, in multinode configuration, there is one namenode and many datanodes.
While setting up for the first time, you initialize namenode by "hdfs namenode -format" then you start datanodes and it works fine.
If you are trying multi-master configuration (multiple namenode running at same time), them i am not sure this will work.
If you are trying active-standby configuration for namenode, you may try below steps
Hadoop Namenode HA setup