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https://issues.apache.org/jira/browse/HDFS-15?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12747115#action_12747115
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Jitendra Nath Pandey commented on HDFS-15:
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In this patch, the blocks will stay in the list, but will not be scheduled for
replication because no new rack would be found to allocate sufficient racks.
Suggestion from Hairong:
If user doesn't specify a topology script for rack
determination, we can ignore the check for enough racks.
We can implement it by checking for config variable SCRIPT_FILENAME_KEY in
blockHasEnoughRacks function. If this config key returns null
blockHasEnoughRacks will return true, which will effectively eliminate the
check for enough racks.
> 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-15.patch.2
>
>
> 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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