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https://issues.apache.org/jira/browse/HDFS-854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12803480#action_12803480
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Zlatin Balevsky commented on HDFS-854:
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If it is not possible to move the i/o operations listFiles() and length()
outside of the lock, it would make sense to set a flag that a block report is
in progress so that the rest of the datanode doesn't just hang. My 2c.
> Datanode should scan devices in parallel to generate block report
> -----------------------------------------------------------------
>
> Key: HDFS-854
> URL: https://issues.apache.org/jira/browse/HDFS-854
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: data-node
> Reporter: dhruba borthakur
>
> A Datanode should scan its disk devices in parallel so that the time to
> generate a block report is reduced. This will reduce the startup time of a
> cluster.
> A datanode has 12 disk (each of 1 TB) to store HDFS blocks. There is a total
> of 150K blocks on these 12 disks. It takes the datanode upto 20 minutes to
> scan these devices to generate the first block report.
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