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https://issues.apache.org/jira/browse/HBASE-7647?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13562128#comment-13562128
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Lars Hofhansl commented on HBASE-7647:
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Good catch. Post mortem +1
                
> 0.94 hfiles v2.1 are not backwards compatible with HFilev2.0
> ------------------------------------------------------------
>
>                 Key: HBASE-7647
>                 URL: https://issues.apache.org/jira/browse/HBASE-7647
>             Project: HBase
>          Issue Type: Bug
>          Components: HFile
>    Affects Versions: 0.94.4
>            Reporter: Elliott Clark
>            Assignee: Elliott Clark
>             Fix For: 0.94.5
>
>         Attachments: HBASE-7647-2.patch
>
>
> When doing a rolling re-start from 0.92.x to 0.94.x any hfiles written by 
> 0.94 are incompatibile with any of the 0.92 region servers.  This is caused 
> by the checksums being put into 0.94.
> * a minor version was added
> * checksums were put into the block
> * checksum meta data was added to block headers.
> I propose that since these changes are only needed if using 
> hbase.regionserver.checksum.verify, they should be turned off if that option 
> is turned off.  Doing so will allow rolling upgrades to go smoother.
> If a user wants to go from a 0.92 cluster to a 0.94 cluster with 
> hbase.regionserver.checksum.verify they can:
> * Roll out 0.94
> * Change hbase-site.xml
> * roll restart the region servers.

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