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https://issues.apache.org/jira/browse/HDFS-15?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12745703#action_12745703
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Raghu Angadi commented on HDFS-15:
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> If we go with only one list, add, remove, update, getPriority methods in
> UnderReplicatedBlocks.java, will need to have another argument to pass the
> numberOfRacks or a boolean to denote insufficient racks. And these methods
> will change to take into account the rack policy. I agree, in that case we
> should rename this class.
Not required according to definition above : "Priority 3: All other
under-replicated blocks." . I.e. you don't need need the extra args. Note that
underreplicated interface already takes "expectedReplicas" as argument
(required for deciding priority).
"Special treatment" is required irrespective of which list it lies in, because
we were not handling this condition before and we need to now.
> All replicas of a block end up on only 1 rack
> ---------------------------------------------
>
> Key: HDFS-15
> URL: https://issues.apache.org/jira/browse/HDFS-15
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Hairong Kuang
> Assignee: Jitendra Nath Pandey
> Priority: Critical
> Attachments: HDFS-15.patch
>
>
> HDFS replicas placement strategy guarantees that the replicas of a block
> exist on at least two racks when its replication factor is greater than one.
> But fsck still reports that the replicas of some blocks end up on one rack.
> The cause of the problem is that decommission and corruption handling only
> check the block's replication factor but not the rack requirement. When an
> over-replicated block loses a replica due to decomission, corruption, or
> heartbeat lost, namenode does not take any action to guarantee that remaining
> replicas are on different racks.
>
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