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From "Zlatin Balevsky (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-854) Datanode should scan devices in parallel to generate block report
Date Thu, 21 Jan 2010 20:45:54 GMT

    [ https://issues.apache.org/jira/browse/HDFS-854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12803480#action_12803480
] 

Zlatin Balevsky commented on HDFS-854:
--------------------------------------

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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