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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3392) Corrupted blocks leading to job failures
Date Wed, 21 May 2008 20:49:55 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3392?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12598782#action_12598782
] 

dhruba borthakur commented on HADOOP-3392:
------------------------------------------

If a block is smaller than its intended size, then just recomputing checksum for that block
will not work, especially if the block is in th middle of the file. It will cause the file
to have blocks that are variable size, and will break many other peices of file-ssytem functionality.

One way to fix a corrupted file is to retrieve the original file (with -ignoreCrc) option
and then copying it back to HDFS. 

> Corrupted blocks leading to job failures
> ----------------------------------------
>
>                 Key: HADOOP-3392
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3392
>             Project: Hadoop Core
>          Issue Type: Improvement
>    Affects Versions: 0.16.0
>            Reporter: Christian Kunz
>
> On one of our clusters we ended up with 11 singly-replicated corrupted blocks (checksum
errors) such that jobs were failing because of no live blocks available.
> fsck reports the system as healthy, although it is not.
> I argue that fsck should have an option to check whether under-replicated blocks are
okay.
> Even better, the namenode should automatically check under-replicated blocks with repeated
replication failures for corruption and list them somewhere on the GUI. And for checksum errors,
there should be an option to undo the corruption and recompute the checksums.
> Question: Is it at all probable that two or more replications of a block have checksum
errors? If not, then we could reduce the checking to singly-replicated blocks.

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