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https://issues.apache.org/jira/browse/HDFS-10887?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15524347#comment-15524347
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Yongjun Zhang commented on HDFS-10887:
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Many thanks [~kihwal]! Very helpful information!
{quote}
By simply dumping the blocksmap, you will find which blocks are being affected,
but where do you go from there? How do you identify the datanodes that are not
reporting?
{quote}
What I was thinking: we can issue a "find blk_..." command passwordlessly to
all datanodes and see which DNs have the block. And for DNs have the block,
then check DN logs to see what the DNs are doing and why block report was not
sent.
Together with this info found, then check the dead DN list, it will give a good
reason why we don't have block report for the block of interest.
Do that make sense to you?
Thanks.
> Provide admin/debug tool to dump block map
> ------------------------------------------
>
> Key: HDFS-10887
> URL: https://issues.apache.org/jira/browse/HDFS-10887
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: hdfs, namenode
> Reporter: Yongjun Zhang
> Assignee: Yongjun Zhang
> Attachments: HDFS-10887.001.patch, HDFS-10887.002.patch
>
>
> From time to time, when NN restarts, we see
> {code}
> "The reported blocks X needs additional Y blocks to reach the threshold
> 0.9990 of total blocks Z. Safe mode will be turned off automatically.
> {code}
> We'd wonder what these blocks that still need block reports are, and what DNs
> they could possibly be located, what happened to these DNs.
> This jira to to propose a new admin or debug tool to dump the block map info
> with the blocks that have fewer than minRepl replicas.
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