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https://issues.apache.org/jira/browse/HDFS-1476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12924724#action_12924724
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dhruba borthakur commented on HDFS-1476:
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We can first enhance the FSNamesystem.listCorruptFileBlocks() to return a
correct list of files even when the namenode is in safemode. It can make one
pass over all the blocks in the BlocksMap and return only those blocks that do
not have any replicas. We can then measure the time it takes to make this RPC,
and depending on its performance we can decide whether to parallelize it or not.
> listCorruptFileBlocks should be functional while the name node is still in
> safe mode
> ------------------------------------------------------------------------------------
>
> Key: HDFS-1476
> URL: https://issues.apache.org/jira/browse/HDFS-1476
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Patrick Kling
>
> This would allow us to detect whether missing blocks can be fixed using Raid
> and if that is the case exit safe mode earlier.
> One way to make listCorruptFileBlocks available before the name node has
> exited from safe mode would be to perform a scan of the blocks map on each
> call to listCorruptFileBlocks to determine if there are any blocks with no
> replicas. This scan could be parallelized by dividing the space of block IDs
> into multiple intervals than can be scanned independently.
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