多次format namenode后，datanode无法正常启动

DataNode报错日志如下：

2021-07-05 16:30:53,595 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool <registering> (Datanode Uuid unassigned) service to test-hadoop-2-21/192.168.2.21:8020. Exiting. 
java.io.IOException: All specified directories are failed to load.
        at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:477)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1361)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1326)
        at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:316)
        at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:223)
        at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:801)
        at java.lang.Thread.run(Thread.java:748)
2021-07-05 16:30:53,597 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool <registering> (Datanode Uuid unassigned) service to test-hadoop-2-21/192.168.2.21:8020
2021-07-05 16:30:53,595 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool <registering> (Datanode Uuid unassigned) service to test-hadoop-2-22/192.168.2.22:8020. Exiting. 
java.io.IOException: Cluster IDs not matched: dn cid=CID-ae173266-e1e1-4871-9b15-f29a7c16e302 but ns cid=CID-0a73391e-ebcc-42ca-99a6-1454d873bb5e; bpid=BP-1650383988-192.168.2.22-1625473706063
        at org.apache.hadoop.hdfs.server.datanode.DataNode.setClusterId(DataNode.java:717)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1319)
        at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:316)
        at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:223)
        at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:801)
        at java.lang.Thread.run(Thread.java:748)
2021-07-05 16:30:53,598 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool <registering> (Datanode Uuid unassigned) service to test-hadoop-2-22/192.168.2.22:8020
2021-07-05 16:30:53,699 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Removed Block pool <registering> (Datanode Uuid unassigned)
2021-07-05 16:30:55,699 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Exiting Datanode
2021-07-05 16:30:55,701 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 0
2021-07-05 16:30:55,703 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: SHUTDOWN_MSG: 

DataNode无法正常启动的话，可以先删除对应的 /xxxx/dfs/data/current 目录  因为version版本不一致导致启动失败。删除成功后，然后重启DataNode。发现重启成功。

然后访问hadoop namenode节点50070端口，发现active和standby节点展示DataNode节点不一样（或者有其中一个直接不展示），则需要同步namenode节点信息保持一致。

如果是在hadoop01节点执行的格式化操作：hdfs namenode -format ，则需要在另一台namenode节点执行同步：hdfs namenode -bootstrapStandby

参考：

https://blog.csdn.net/QMW19910301/article/details/78055601

https://blog.51cto.com/hsbxxl/2066487