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https://issues.apache.org/jira/browse/HDFS-13709?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16911526#comment-16911526
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Chen Zhang commented on HDFS-13709:
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Got it, thanks [~jojochuang] for your explanation.
> Report bad block to NN when transfer block encounter EIO exception
> ------------------------------------------------------------------
>
> Key: HDFS-13709
> URL: https://issues.apache.org/jira/browse/HDFS-13709
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Chen Zhang
> Assignee: Chen Zhang
> Priority: Major
> Fix For: 3.3.0, 3.2.1, 3.1.3
>
> Attachments: HDFS-13709.002.patch, HDFS-13709.003.patch,
> HDFS-13709.004.patch, HDFS-13709.005.patch, HDFS-13709.patch
>
>
> In our online cluster, the BlockPoolSliceScanner is turned off, and sometimes
> disk bad track may cause data loss.
> For example, there are 3 replicas on 3 machines A/B/C, if a bad track occurs
> on A's replica data, and someday B and C crushed at the same time, NN will
> try to replicate data from A but failed, this block is corrupt now but no one
> knows, because NN think there is at least 1 healthy replica and it keep
> trying to replicate it.
> When reading a replica which have data on bad track, OS will return an EIO
> error, if DN reports the bad block as soon as it got an EIO, we can find
> this case ASAP and try to avoid data loss
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