Jing Zhao created HDFS-9866:
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             Summary: BlockManager#chooseExcessReplicasStriped may weaken rack 
fault tolerance
                 Key: HDFS-9866
                 URL: https://issues.apache.org/jira/browse/HDFS-9866
             Project: Hadoop HDFS
          Issue Type: Sub-task
          Components: namenode
    Affects Versions: 3.0.0
            Reporter: Takuya Fukudome
            Assignee: Jing Zhao


In [~tfukudom]'s system tests, we find the following issue:

A striped block group B has redundant internal block replicas. 9 internal 
blocks are stored in 10 datanodes across 6 racks. Datanode d1 and d2 both store 
a replica for internal block b1. d1's rack contains multiple internal blocks 
while d2's rack only has b1. Then when choosing a duplicated replica to delete, 
 the current implementation may wrongly choose d2 thus causes the total number 
of racks to be decreased to 5.



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