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https://issues.apache.org/jira/browse/HDFS-11609?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15954245#comment-15954245
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Kihwal Lee commented on HDFS-11609:
-----------------------------------
bq. I have a patch with 1) and a unit test, but want to hear from others before
posting.
I thought it is acceptable to simply let admins know something is wrong
(instead of pretending everything is fine), but then the recovery would be hard
for many people, especially if it involves many nodes and blocks. So it might
be better to automatically recover as much as possible. The version of patch I
am attaching now considers a decommissioned node as a replication source if
there is no live node. I.e. implementing the option 3). 1) is not done here, as
it makes replication not happen.
> Some blocks can be permanently lost if nodes are decommissioned while dead
> --------------------------------------------------------------------------
>
> Key: HDFS-11609
> URL: https://issues.apache.org/jira/browse/HDFS-11609
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.7.0
> Reporter: Kihwal Lee
> Assignee: Kihwal Lee
> Priority: Critical
>
> When all the nodes containing a replica of a block are decommissioned while
> they are dead, they get decommissioned right away even if there are missing
> blocks. This behavior was introduced by HDFS-7374.
> The problem starts when those decommissioned nodes are brought back online.
> The namenode no longer shows missing blocks, which creates a false sense of
> cluster health. When the decommissioned nodes are removed and reformatted,
> the block data is permanently lost. The namenode will report missing blocks
> after the heartbeat recheck interval (e.g. 10 minutes) from the moment the
> last node is taken down.
> There are multiple issues in the code. As some cause different behaviors in
> testing vs. production, it took a while to reproduce it in a unit test. I
> will present analysis and proposal soon.
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