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From "Dmytro Molkov (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1476) listCorruptFileBlocks should be functional while the name node is still in safe mode
Date Mon, 25 Oct 2010 21:30:19 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12924729#action_12924729
] 

Dmytro Molkov commented on HDFS-1476:
-------------------------------------

I think the parallelism here will depend on multiple different characteristics: the number
of cores in the system, the size of the blocks map, maybe others. So it might make sense to
make this one configurable to begin with. Large clusters will certainly benefit from running
multiple parallel threads since the time to scan full BlocksMap will be in minutes.

> 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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