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https://issues.apache.org/jira/browse/HDFS-6729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14074651#comment-14074651
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Colin Patrick McCabe commented on HDFS-6729:
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By default it takes 10 and a half minutes until the NameNode starts
re-replicating anything. With the stale DN feature turned on, applications
trying to read from the stale node will be re-directed, so the cluster won't
experience lag (or at least, not because of applications trying to contact the
node under maintenance).
So I guess the question is, is it worth adding another state in case the
maintenance on the datanode can't be finished in 10 minutes? On the upside, I
suppose it probably wouldn't be a lot of code. It would be very similar to the
stale datanode stuff we already implemented.
> Support maintenance mode for DN
> -------------------------------
>
> Key: HDFS-6729
> URL: https://issues.apache.org/jira/browse/HDFS-6729
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 2.4.0
> Reporter: Lei (Eddy) Xu
>
> Some maintenance works (e.g., upgrading RAM or add disks) on DataNode only
> takes a short amount of time (e.g., 10 minutes). In these cases, the users do
> not want to report missing blocks on this DN because the DN will be online
> shortly without data lose. Thus, we need a maintenance mode for a DN so that
> maintenance work can be carried out on the DN without having to decommission
> it or the DN being marked as dead.
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