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https://issues.apache.org/jira/browse/HDFS-15560?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17194073#comment-17194073
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Xiaoqiao He commented on HDFS-15560:
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Thanks [~wzx513] for your report, any idea to improve it?
> The getMaxNodesPerRack May Cause "Failed to place enough replicas"
> ------------------------------------------------------------------
>
> Key: HDFS-15560
> URL: https://issues.apache.org/jira/browse/HDFS-15560
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: wangzhixiang
> Assignee: wangzhixiang
> Priority: Major
>
> In our hdfs Cluster, the nodes in each rack is extremely uneven.
> Eg. rack1=[1 node], rack2=[1 node], rack3=[3 nodes], rack4=[5 nodes],
> rack5=[4 nodes], rack6=[4 nodes].
> When invoke getMaxNodesPerRack method, we will get MaxNodesPerRack = 4 by
> MaxNodesPerRack = (totalNumOfReplicas-1)/numOfRacks + 2, totalNumOfReplicas =
> 18, numOfRacks = 6。
> And the replications of some files in our cluster is set to 50, so it be
> allocated 18 replicas and we need the all nodes . However, the rack4 could
> only choose 4 nodes because of MaxNodesPerRack = 4. It will cause only 17
> (1+1+3+4+4+4) replicas be choosen and throws the warn log "Failed to place
> enough replicas, still in need of 1 to reach 18".
> Besides, ReplicationMonitor will add the file as ReplicationWork to retry and
> it still failed in loop.
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