Steve Loughran created HADOOP-15297:
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             Summary: Make s3a etag -> checksum publishing option
                 Key: HADOOP-15297
                 URL: https://issues.apache.org/jira/browse/HADOOP-15297
             Project: Hadoop Common
          Issue Type: Sub-task
          Components: fs/s3
    Affects Versions: 3.1.0
            Reporter: Steve Loughran
            Assignee: Steve Loughran


HADOOP-15273 shows how distcp doesn't handle non-HDFS filesystems with 
checksums.

Exposing Etags as checksums, HADOOP-13282, breaks workflows which back up to 
s3a.

Rather than revert  I want to make it an option, off by default. Once we are 
happy with distcp in future, we can turn it on.

Why an option? Because it lines up for a successor to distcp which saves src 
and dest checksums to a file and can then verify whether or not files have 
really changed. Currently distcp relies on dest checksum algorithm being the 
same as the src for incremental updates, but if either of the stores don't 
serve checksums, silently downgrades to not checking. 




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