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https://issues.apache.org/jira/browse/HDFS-16146?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated HDFS-16146:
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Labels: pull-request-available (was: )
> All three replicas are lost due to not adding a new DataNode in time
> --------------------------------------------------------------------
>
> Key: HDFS-16146
> URL: https://issues.apache.org/jira/browse/HDFS-16146
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode, hdfs
> Reporter: Shuyan Zhang
> Assignee: Shuyan Zhang
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> We have a three-replica file, and all replicas of a block are lost when the
> default datanode replacement strategy is used. It happened like this:
> 1. addBlock() applies for a new block and successfully connects three
> datanodes (dn1, dn2 and dn3) to build a pipeline;
> 2. Write data;
> 3. dn1 has an error and was kicked out. At this time, the remaining datanodes
> in the pipeline > 1, according to the replacement strategy, there is no need
> to add a new datanode;
> 4. After writing is completed, enter PIPELINE_CLOSE;
> 5. dn2 has an error and was kicked out. But because it is already in the
> close phase, addDatanode2ExistingPipeline() decides to hand over the task of
> transfering the replica to the NameNode. At this time, there is only one
> datanode left in the pipeline;
> 6. dn3 error, all replicas are lost.
> If we add a new datanode in step 5, we can avoid losing all replicas in this
> case. I think error in PIPELINE_CLOSE and error in DATA_STREAMING have the
> same risk of losing replicas, we should not skip adding a new datanode
> during PIPELINE_CLOSE.
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