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https://issues.apache.org/jira/browse/HADOOP-2012?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12534137
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Sameer Paranjpye commented on HADOOP-2012:
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> Many disk errors occur during the write path. If we modify .meta file that
> contains .crc every few days, we might actually increase error rate.
Would writing more to the .meta file increase the chance of the .meta file
being corrupted? I'm not sure I see that.
> Also writing to metafile will be at least one random seek/write for each
> verification.
This matters only if the validation is done very frequently. The scheme
proposed here suggests slow background checking. Do we really need to check
more than a few blocks an hour?
> 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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