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https://issues.apache.org/jira/browse/HDFS-9023?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14730719#comment-14730719
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Surendra Singh Lilhore commented on HDFS-9023:
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In log we can give some extra info to client like {{READ_ONLY=10, NO_SPACE=5,
FAILED=4}} OR {{All required storage types are unavailable.}}
> When NN is not able to identify DN for replication, reason behind it can be
> logged
> ----------------------------------------------------------------------------------
>
> Key: HDFS-9023
> URL: https://issues.apache.org/jira/browse/HDFS-9023
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client, namenode
> Affects Versions: 2.7.1
> Reporter: Surendra Singh Lilhore
> Assignee: Surendra Singh Lilhore
> Priority: Critical
>
> When NN is not able to identify DN for replication, reason behind it can be
> logged (at least critical information why DNs not chosen like disk is full).
> At present it is expected to enable debug log.
> For example the reason for below error looks like all 7 DNs are busy for data
> writes. But at client or NN side no hint is given in the log message.
> {noformat}
> File /tmp/logs/spark/logs/application_1437051383180_0610/xyz-195_26009.tmp
> could only be replicated to 0 nodes instead of minReplication (=1). There
> are 7 datanode(s) running and no node(s) are excluded in this operation.
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget4NewBlock(BlockManager.java:1553)
>
> {noformat}
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