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https://issues.apache.org/jira/browse/HADOOP-2012?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12534146
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Raghu Angadi commented on HADOOP-2012:
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Without appends, a block and .meta file are written to only once. With this,
.meta will be written to many times. Ignoring appends, probability of write
corruption for a given byte around the 'last verification time' would be
orders of magnitude *more* than other data on the disk and not less.
I will increase the .meta version and write this information at the the
beginning of the file. I am still not very sure of benifits of persisting the
verification time.. but there might be more.
> 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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