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https://issues.apache.org/jira/browse/HDFS-3225?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13248744#comment-13248744
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Sanjay Radia commented on HDFS-3225:
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HDFS's upgrade snapshot feature is a unique and powerful part upgrading HDFS
across versions.
An HDFS upgrade involves snapshots of the data on NN and DNs. Upgrade Snapshots
are not just for layout changes but also for data protection against a version
change that introduces a bug that wipes out a portion or all of the data.
(Other systems ask the admin to do a backup before starting the upgrade - that
does not make sense for HDFS).
For example, Yahoo does snapshot as part of all upgrades, except for minor
fixes such as Emergency-Bug-Fixes.
We need to revisit upgrade snapshots in light of rolling upgrades.
> Revist upgrade snapshots, roll back, finalize to enable rolling upgrades
> ------------------------------------------------------------------------
>
> Key: HDFS-3225
> URL: https://issues.apache.org/jira/browse/HDFS-3225
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Sanjay Radia
>
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