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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-2012) Periodic verification at the Datanode
Date Fri, 19 Oct 2007 18:33:50 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-2012?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Raghu Angadi updated HADOOP-2012:
---------------------------------

    Attachment: HADOOP-2012.patch

Attaching the patch for review.

- Currently the period is 2 weeks. Not configurable
- This patch does not throttle yet. Will need throttler from HADOOP-1912. It will be simple
mod to add it.
- This patch does not store the last scan times persistently. How we want to modify meta file
will be clearer once we have better picture of how it is affected by append feature.

- This does not have a unit test yet. For unit test, we need to make the SCAN_PERIOD configurable.



> 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
>         Attachments: HADOOP-2012.patch
>
>
> 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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