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Date: Tue, 24 May 2016 14:57:12 +0000 (UTC)
From: "Kai Zheng (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12940402.1455863698000.277227.1464101832872@Atlassian.JIRA>
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References: <JIRA.12940402.1455863698000@Atlassian.JIRA> <JIRA.12940402.1455863698525@arcas>
Subject: [jira] [Commented] (HDFS-9833) Erasure coding: recomputing block
 checksum on the fly by reconstructing the missed/corrupt block data
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archived-at: Tue, 24 May 2016 14:57:14 -0000


    [ https://issues.apache.org/jira/browse/HDFS-9833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15298307#comment-15298307 ] 

Kai Zheng commented on HDFS-9833:
---------------------------------

Thanks Rakesh for the update on this. I will take a careful review tomorrow. Sounds good to me to do the tasks split up and would you please go ahead. 

> Erasure coding: recomputing block checksum on the fly by reconstructing the missed/corrupt block data
> -----------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-9833
>                 URL: https://issues.apache.org/jira/browse/HDFS-9833
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Kai Zheng
>            Assignee: Rakesh R
>              Labels: hdfs-ec-3.0-must-do
>         Attachments: HDFS-9833-00-draft.patch, HDFS-9833-01.patch, HDFS-9833-02.patch, HDFS-9833-03.patch, HDFS-9833-04.patch
>
>
> As discussed in HDFS-8430 and HDFS-9694, to compute striped file checksum even some of striped blocks are missed, we need to consider recomputing block checksum on the fly for the missed/corrupt blocks. To recompute the block checksum, the block data needs to be reconstructed by erasure decoding, and the main needed codes for the block reconstruction could be borrowed from HDFS-9719, the refactoring of the existing {{ErasureCodingWorker}}. In EC worker, reconstructed blocks need to be written out to target datanodes, but here in this case, the remote writing isn't necessary, as the reconstructed block data is only used to recompute the checksum.


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