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https://issues.apache.org/jira/browse/HDFS-4758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13642280#comment-13642280
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Suresh Srinivas commented on HDFS-4758:
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The current branch does support nested snapshots. The reason why this is being
proposed is to provide limited functionality early on and if that suffices
remove complexity associated with supporting and testing nested snapshots at
arbitrary levels. If we support nested snapshots now, it will not be possible
to take it away in the future. In my discussion with Jing and Nicholas we had
considered the following:
# Allow snapshot of / as a special case and that is the only snapshottable
directory with in which another snapshottable directory is allowed.
# Disallow nested snapshots in the first phase. See how how this is used by the
users and enable it either as stated in the first bullet or remove the
restriction altogether.
If the current restrictions takes away some use cases, so be it. Lets turn it
back on later if we cannot live without it.
> Disallow nested snapshottable directories
> -----------------------------------------
>
> Key: HDFS-4758
> URL: https://issues.apache.org/jira/browse/HDFS-4758
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
>
> Nested snapshottable directories are supported by the current implementation.
> However, it seems that there are no good use cases for nested snapshottable
> directories. So we disable it for now until someone has a valid use case for
> it.
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