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https://issues.apache.org/jira/browse/HDFS-1271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12883655#action_12883655
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dhruba borthakur commented on HDFS-1271:
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This is a *real* problem that we have faced on our clusters's too.
> Decommissioning nodes not persisted between NameNode restarts
> -------------------------------------------------------------
>
> Key: HDFS-1271
> URL: https://issues.apache.org/jira/browse/HDFS-1271
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: name-node
> Reporter: Travis Crawford
>
> Datanodes in the process of being decomissioned should still be
> decomissioning after namenode restarts. Currently they are marked as dead
> after a restart.
> Details:
> Nodes can be safely removed from a cluster by marking them as decomissioned
> and waiting for their data to be replicated elsewhere. This is accomplished
> by adding a node to the filed referenced by dfs.hosts.excluded, then
> refreshing nodes.
> Decomissioning means block reports from the decomissioned datanode are no
> longer accepted by the namenode, meaning for decomissioning to occur the NN
> must have an existing block report. That is, a datanode can transition from:
> live --> decomissioning --> dead. Nodes can NOT transition from: dead -->
> decomissioning --> dead.
> Operationally this is problematic because intervention is required should the
> NN restart while nodes are decomissioning, meaning in-house administration
> tools must be more complex, or more likely admins have to babysit the
> decomissioning process.
> Someone more familiar with the code might have a better idea, but perhaps the
> first block report for dfs.hosts.excluded hosts should be accepted?
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