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https://issues.apache.org/jira/browse/HDFS-4288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13531213#comment-13531213
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Daryn Sharp commented on HDFS-4288:
-----------------------------------
Non-23 branches appear to have a rudimentary fix for this issue. However it
appears (haven't tested) that if a node registers in safe mode with 500 blocks,
then bounces and re-registers with only 100 blocks because maybe a disk died,
the NN will ignore that BR if it's still in safemode. The NN may come out of
safe mode w/o realizing it doesn't really have all the replicas it needs, and
probably won't issue replications until the next full BR is sent which
increases the possibility of data loss.
> NN accepts incremental BR as IBR in safemode
> --------------------------------------------
>
> Key: HDFS-4288
> URL: https://issues.apache.org/jira/browse/HDFS-4288
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 0.23.0, 2.0.0-alpha, 3.0.0
> Reporter: Daryn Sharp
> Assignee: Daryn Sharp
> Priority: Critical
>
> If a DN is ready to send an incremental BR and the NN goes down, the DN will
> repeatedly try to reconnect. The NN will then process the DN's incremental
> BR as an initial BR. The NN now thinks the DN has only a few blocks, and
> will ignore all subsequent BRs from that DN until out of safemode -- which it
> may never do because of all the "missing" blocks on the affected DNs.
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