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From "Jakob Homan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-854) Datanode should scan devices in parallel to generate block report
Date Wed, 24 Mar 2010 21:59:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12849476#action_12849476

Jakob Homan commented on HDFS-854:

The test failure is not related in all likelihood.  The patch overall looks good. 
One change: dfs.datanode.directoryscan.threads should be defined and referenced via DFSConfigKeys.java.
One question: Is it appropriate to just log the error when compiling block reports (line 125
in patch), or should more drastic action be taken?
One request: Naming patches with a final number really confuses all my editors, how about
HDFS-854-1.patch (although numbering patches is greatly appreciated!)

> 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
>    Affects Versions: 0.22.0
>            Reporter: dhruba borthakur
>            Assignee: Dmytro Molkov
>             Fix For: 0.22.0
>         Attachments: HDFS-854.patch, HDFS-854.patch.1
> 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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