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https://issues.apache.org/jira/browse/HADOOP-2012?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12535712
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Raghu Angadi commented on HADOOP-2012:
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> From what I know it's the Namenode, which I believe doesn't do anything with
> the reports other than logging the failure.
Namenode actually deletes the block if there are more than one copy. Periodic
verification uses that same RPC.
> It would be better to report the failure to the Datanode, have the Datanode
> validate what's on disk and report corruption to the Namenode if the
> validation fails.
I agree. This will avoid spurious block deletion during in memory corruption.
> Periodic verification at the Datanode
> -------------------------------------
>
> Key: HADOOP-2012
> URL: https://issues.apache.org/jira/browse/HADOOP-2012
> Project: Hadoop
> Issue Type: New Feature
> Components: dfs
> Reporter: Raghu Angadi
> Assignee: Raghu Angadi
>
> Currently on-disk data corruption on data blocks is detected only when it is
> read by the client or by another datanode. These errors are detected much
> earlier if datanode can periodically verify the data checksums for the local
> blocks.
> Some of the issues to consider :
> - How should we check the blocks ( no more often than once every couple of
> weeks ?)
> - How do we keep track of when a block was last verfied ( there is a .meta
> file associcated with each lock ).
> - What action to take once a corruption is detected
> - Scanning should be done as a very low priority with rest of the datanode
> disk traffic in mind.
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