问题描述:

I'm getting the following error when attempting to write to HDFS as part of my multi-threaded application

could only be replicated to 0 nodes instead of minReplication (=1). There are 1 datanode(s) running and no node(s) are excluded in this operation.

I've tried the top-rated answer here around reformatting but this doesn't work for me: HDFS error: could only be replicated to 0 nodes, instead of 1

What is happening is this:

  1. My application consists of 2 threads each one configured with their own Spring Data PartitionTextFileWriter
  2. Thread 1 is the first to process data and this can successfully write to HDFS
  3. However, once Thread 2 starts to process data I get this error when it attempts to flush to a file

Thread 1 and 2 will not be writing to the same file, although they do share a parent directory at the root of my directory tree.

There are no problems with disk space on my server.

I also see this in my name-node logs, but not sure what it means:

2016-03-15 11:23:12,149 WARN org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy: Failed to place enough replicas, still in need of 1 to reach 1 (unavailableStorages=[], storagePolicy=BlockStoragePolicy{HOT:7, storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]}, newBlock=true) For more information, please enable DEBUG log level on org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy

2016-03-15 11:23:12,150 WARN org.apache.hadoop.hdfs.protocol.BlockStoragePolicy: Failed to place enough replicas: expected size is 1 but only 0 storage types can be selected (replication=1, selected=[], unavailable=[DISK], removed=[DISK], policy=BlockStoragePolicy{HOT:7, storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]})

2016-03-15 11:23:12,150 WARN org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy: Failed to place enough replicas, still in need of 1 to reach 1 (unavailableStorages=[DISK], storagePolicy=BlockStoragePolicy{HOT:7, storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]}, newBlock=true) All required storage types are unavailable: unavailableStorages=[DISK], storagePolicy=BlockStoragePolicy{HOT:7, storageTypes=[DISK], creationFallbacks=[], replicationFallbacks=[ARCHIVE]}

2016-03-15 11:23:12,151 INFO org.apache.hadoop.ipc.Server: IPC Server handler 8 on 9000, call org.apache.hadoop.hdfs.protocol.ClientProtocol.addBlock from 10.104.247.78:52004 Call#61 Retry#0

java.io.IOException: File /metrics/abc/myfile could only be replicated to 0 nodes instead of [2016-03-15 13:34:16,663] INFO [Group Metadata Manager on Broker 0]: Removed 0 expired offsets in 1 milliseconds. (kafka.coordinator.GroupMetadataManager)

What could be the cause of this error?

Thanks

网友答案:

This error is caused by the block replication system of HDFS since it could not manage to make any copies of a specific block within the focused file. Common reasons of that:

  1. Only a NameNode instance is running and it's not in safe-mode
  2. There is no DataNode instances up and running, or some are dead. (Check the servers)
  3. Namenode and Datanode instances are both running, but they cannot communicate with each other, which means There is connectivity issue between DataNode and NameNode instances.
  4. Running DataNode instances are not able to talk to the server because of some networking of hadoop-based issues (check logs that include datanode info)
  5. There is no hard disk space specified in configured data directories for DataNode instances or DataNode instances have run out of space. (check dfs.data.dir // delete old files if any)
  6. Specified reserved spaces for DataNode instances in dfs.datanode.du.reserved is more than the free space which makes DataNode instances to understand there is no enough free space.
  7. There is no enough threads for DataNode instances (check datanode logs and dfs.datanode.handler.count value)
  8. Make sure dfs.data.transfer.protection is not equal to “authentication” and dfs.encrypt.data.transfer is equal to true.

Also please:

  • Verify the status of NameNode and DataNode services and check the related logs
  • Verify if core-site.xml has correct fs.defaultFS value and hdfs-site.xml has a valid value.
  • Verify hdfs-site.xml has dfs.namenode.http-address.. for all NameNode instances specified in case of PHD HA configuration.
  • Verify if the permissions on the directories are correct

Ref: https://wiki.apache.org/hadoop/CouldOnlyBeReplicatedTo

Ref: https://support.pivotal.io/hc/en-us/articles/201846688-HDFS-reports-Configured-Capacity-0-0-B-for-datanode

Also, please check: Writing to HDFS from Java, getting "could only be replicated to 0 nodes instead of minReplication"

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