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https://issues.apache.org/jira/browse/HDFS-14465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16834534#comment-16834534
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Yicong Cai commented on HDFS-14465:
-----------------------------------
[^HDFS-14465.02.patch] Fix checkstyle.
Had tested the hadoop.hdfs.web.TestWebHdfsTimeouts use case separately and it
works fine.
> When the Block expected replications is larger than the number of DataNodes,
> entering maintenance will never exit.
> ------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-14465
> URL: https://issues.apache.org/jira/browse/HDFS-14465
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.9.2
> Reporter: Yicong Cai
> Priority: Major
> Attachments: HDFS-14465.01.patch, HDFS-14465.02.patch
>
>
> Scenes:
> There is a small HDFS cluster with 5 DataNodes; one of them is maintained,
> added to the maintenance list, and set
> dfs.namenode.maintenance.replication.min to 1.
> When refresh Nodes, the NameNode starts checking whether the blocks on the
> node require a new replication.
> The replications of the MapReduce task job file is 10 by default,
> isNeededReplicationForMaintenance will determine to false, and
> isSufficientlyReplicated will determine to false, so the block of the job
> file needs to increase the replication.
> When adding a replication, since the cluster has only 5 DataNodes, all the
> nodes have the replications of the block, chooseTargetInOrder will throw a
> NotEnoughReplicasException, so that the replication cannot be increase, and
> the Entering Maintenance cannot be ended.
> This issue will cause the independent small cluster to be unable to use the
> maintenance mode.
>
> {panel:title=chooseTarget exception log}
> 2019-05-03 23:42:31,008 [31545331] - WARN
> [ReplicationMonitor:BlockPlacementPolicyDefault@431] - Failed to place enough
> replicas, still in need of 1 to reach 5 (unavailableStorages=[],
> storagePolicy=BlockStoragePolicy\{HOT:7, storageTypes=[DISK],
> creationFallbacks=[], replicationFallbacks=[ARCHIVE]}, newBlock=false) For
> more information, please enable DEBUG log level on
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy and
> org.apache.hadoop.net.NetworkTopology
> {panel}
>
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