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https://issues.apache.org/jira/browse/HDFS-12643?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17421255#comment-17421255
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TisNotT commented on HDFS-12643:
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it is confuse to me too.So I am finding whether there is an api to set special
datanodes to maintenance state or not. If not,maybe I will dev one for my
company.
> HDFS maintenance state behaviour is confusing and not well documented
> ---------------------------------------------------------------------
>
> Key: HDFS-12643
> URL: https://issues.apache.org/jira/browse/HDFS-12643
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: documentation, namenode
> Reporter: Andre Araujo
> Priority: Major
>
> The current implementation of the HDFS maintenance state feature is confusing
> and error-prone. The documentation is missing important information that's
> required for the correct use of the feature.
> For example, if the Hadoop admin wants to put a single node in maintenance
> state, he/she can add a single entry to the maintenance file with the
> contents:
> {code}
> {
> "hostName": "host-1.example.com",
> "adminState": "IN_MAINTENANCE",
> "maintenanceExpireTimeInMS": 1507663698000
> }
> {code}
> Let's say now that the actual maintenance finished well before the set
> expiration time and the Hadoop admin wants to bring the node back to NORMAL
> state. It would be natural to simply change the state of the node, as show
> below, and run another refresh:
> {code}
> {
> "hostName": "host-1.example.com",
> "adminState": "NORMAL"
> }
> {code}
> The configuration file above, though, not only take the node {{host-1}} out
> of maintenance state but it also *blacklists all the other DataNodes*. This
> behaviour seems inconsistent to me and is due to {{emptyInServiceNodeLists}}
> being set to {{false}}
> [here|https://github.com/apache/hadoop/blob/230b85d5865b7e08fb7aaeab45295b5b966011ef/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/CombinedHostFileManager.java#L80]
> only when there is at least one node with {{adminState = NORMAL}} listed in
> the file.
> I believe that it would be more consistent, and less error prone, to simply
> implement the following:
> * If the dfs.hosts file is empty, all nodes are allowed and in normal state
> * If the file is not empty, any host *not* listed in the file is
> *blacklisted*, regardless of the state of the hosts listed in the file.
> Regardless of the implementation being changed or not, the documentation also
> needs to be updated to ensure the readers know of the caveats mentioned above.
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