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https://issues.apache.org/jira/browse/HDFS-7235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14183651#comment-14183651
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Yongjun Zhang commented on HDFS-7235:
-------------------------------------
Hi Colin,
Good catch of yours. When getLength() throws IOException, the pre-existing
behaviour was to issue a warn message from the caller side of
{{DataNode#transferBlock}}, so I was trying to keep that behaviour. But after
discussing with you, I agree that we should report bad block for this scenario
because the block file was not accessible. I just uploaded rev 006 to
incorporate this change. Thanks.
> Can not decommission DN which has invalid block due to bad disk
> ---------------------------------------------------------------
>
> Key: HDFS-7235
> URL: https://issues.apache.org/jira/browse/HDFS-7235
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode, namenode
> Affects Versions: 2.6.0
> Reporter: Yongjun Zhang
> Assignee: Yongjun Zhang
> Attachments: HDFS-7235.001.patch, HDFS-7235.002.patch,
> HDFS-7235.003.patch, HDFS-7235.004.patch, HDFS-7235.005.patch,
> HDFS-7235.006.patch
>
>
> When to decommission a DN, the process hangs.
> What happens is, when NN chooses a replica as a source to replicate data on
> the to-be-decommissioned DN to other DNs, it favors choosing this DN
> to-be-decommissioned as the source of transfer (see BlockManager.java).
> However, because of the bad disk, the DN would detect the source block to be
> transfered as invalidBlock with the following logic in FsDatasetImpl.java:
> {code}
> /** Does the block exist and have the given state? */
> private boolean isValid(final ExtendedBlock b, final ReplicaState state) {
> final ReplicaInfo replicaInfo = volumeMap.get(b.getBlockPoolId(),
> b.getLocalBlock());
> return replicaInfo != null
> && replicaInfo.getState() == state
> && replicaInfo.getBlockFile().exists();
> }
> {code}
> The reason that this method returns false (detecting invalid block) is
> because the block file doesn't exist due to bad disk in this case.
> The key issue we found here is, after DN detects an invalid block for the
> above reason, it doesn't report the invalid block back to NN, thus NN doesn't
> know that the block is corrupted, and keeps sending the data transfer request
> to the same DN to be decommissioned, again and again. This caused an infinite
> loop, so the decommission process hangs.
> Thanks [~qwertymaniac] for reporting the issue and initial analysis.
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