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https://issues.apache.org/jira/browse/HDFS-1655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13014103#comment-13014103
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Jitendra Nath Pandey commented on HDFS-1655:
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This patch removes the REMOTE_READ scan type from the DataBlockScanner. Client
still verifies the block and namenode is informed if any corruption detected,
but the block scanner is not notified to update its scan status for that block.
The reasons:
1. The datanode verification runs in background and should be an independent
verification mechanism internal to the datanode.
2. It is more complicated with federation because block pools are scanned in
round robin and a client might verify a block for a block pool scanner which
may not be running.
3. The goal of the optimization was just to skip verification of the block
which has been read by the client. This optimization doesn't seem to justify
the complexity. Anyway the scanner doesn't verify a block again if it was
recently verified.
> Federation: DatablockScanner should scan blocks for all the block pools.
> ------------------------------------------------------------------------
>
> Key: HDFS-1655
> URL: https://issues.apache.org/jira/browse/HDFS-1655
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Affects Versions: Federation Branch
> Reporter: Jitendra Nath Pandey
> Assignee: Jitendra Nath Pandey
> Fix For: Federation Branch
>
> Attachments: HDFS-1655.1.patch, HDFS-1655.2.patch
>
>
> DataBlockScanner changes are needed to work with federation.
> Goal is to have DataBlockScanner visit one volume at a time, scanning block
> pools under it one at a time.
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