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https://issues.apache.org/jira/browse/HADOOP-3637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12626630#action_12626630
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dhruba borthakur commented on HADOOP-3637:
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I think blocks that belong to snapshots but not to the primary namespace still
needs to be replicated. Similarly, rebalancing,decommission, etc should work
correctly on these blocks. That is the reaosn why my design has a SnapNode that
is used to maintain the blocks of snapshots that are not mounted read-write.
For snapshots that are mounted read-write, it is the ViewNode that serves the
namespace as well as the blocks that contain them.
Regarding Sanjay's comments: The ability to 'time-travel' is not a motivation
for this design. The primary and only motivation is for "disaster recovery".
However, I believe that this design is good for scaling to a v large HDFS
cluster. Pl let me know if you see/need any major changes in the proposed
design.
Regarding Allenn's comments: This design provides for full-file system snapshot
and recovery. Snapshots of specified directories are not allowed. However, one
can specify a set of directories to exclude from a snapshot (to eliminate tmp
directories). In the long term, we can enhance this feature to support
per-directory snapshots.
> Support for snapshots
> ---------------------
>
> Key: HADOOP-3637
> URL: https://issues.apache.org/jira/browse/HADOOP-3637
> Project: Hadoop Core
> Issue Type: New Feature
> Components: dfs
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Attachments: Snapshots.pdf, Snapshots.pdf
>
>
> Support HDFS snapshots. It should support creating snapshots without shutting
> down the file system. Snapshot creation should be lightweight and a typical
> system should be able to support a few thousands concurrent snapshots. There
> should be a way to surface (i.e. mount) a few of these snapshots
> simultaneously.
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