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https://issues.apache.org/jira/browse/HDFS-2699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13171961#comment-13171961
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Todd Lipcon commented on HDFS-2699:
-----------------------------------

The idea of introducing the new format as a backward-compatible option sounds 
good to me. That's what we did for the CRC32C checksums - new files are written 
with that checksum algorithm but old files continue to operate with the old one.
                
> Store data and checksums together in block file
> -----------------------------------------------
>
>                 Key: HDFS-2699
>                 URL: https://issues.apache.org/jira/browse/HDFS-2699
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> The current implementation of HDFS stores the data in one block file and the 
> metadata(checksum) in another block file. This means that every read from 
> HDFS actually consumes two disk iops, one to the datafile and one to the 
> checksum file. This is a major problem for scaling HBase, because HBase is 
> usually  bottlenecked on the number of random disk iops that the 
> storage-hardware offers.

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