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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8233) Turn CRC checking off for 0 byte size and differing blocksizes
Date Mon, 05 Mar 2018 20:36:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8233?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16386728#comment-16386728
] 

Steve Loughran commented on HADOOP-8233:
----------------------------------------

* 0-byte length can be skipped
* blocksize is trouble, as for filesystems != HDFS, there's no guarantee that different blocksize
==> Different checksum.

> Turn CRC checking off for 0 byte size and differing blocksizes
> --------------------------------------------------------------
>
>                 Key: HADOOP-8233
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8233
>             Project: Hadoop Common
>          Issue Type: Bug
>    Affects Versions: 0.23.3
>            Reporter: Dave Thompson
>            Assignee: Dave Thompson
>            Priority: Major
>         Attachments: HADOOP-8233-branch-0.23.2.patch
>
>
> DistcpV2 (hadoop-tools/hadoop-distcp/..) can fail from checksum failure, sometimes when
copying a 0 byte file.    Root cause of this may have to do with an inconsistent nature of
HDFS when creating 0 byte files, however distcp can avoid this issue by not checking CRC when
size is zero.
> Further, distcp fails checksum when copying from two clusters that use different blocksizes.
 In this case it does not make sense to check CRC, as it is a guaranteed failure.
> We need to turn CRC checking off for the above two cases.



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