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https://issues.apache.org/jira/browse/HDFS-6978?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14132544#comment-14132544
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Jitendra Nath Pandey commented on HDFS-6978:
--------------------------------------------
+1
> Directory scanner should correctly reconcile blocks on RAM disk
> ---------------------------------------------------------------
>
> Key: HDFS-6978
> URL: https://issues.apache.org/jira/browse/HDFS-6978
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode
> Affects Versions: HDFS-6581
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Attachments: HDFS-6978.01.patch, HDFS-6978.02.patch
>
>
> It used to be very unlikely that the directory scanner encountered two
> replicas of the same block on different volumes.
> With memory storage, it is very likely to hit this with the following
> sequence of events:
> # Block is written to RAM disk
> # Lazy writer saves a copy on persistent volume
> # DN attempts to evict the original replica from RAM disk, file deletion
> fails as the replica is in use.
> # Directory scanner finds a replica on both RAM disk and persistent storage.
> The directory scanner should never delete the block on persistent storage.
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