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https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13276461#comment-13276461
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M. C. Srivas commented on HDFS-3370:
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Sanjay, POSIX says that a user cannot open a file unless they have permissions
to traverse the entire path from / to the file. The problem is that if a file
has two paths (as in a hard-link), perms becomes very hard to enforce since a
file does not know which dir is its parent. Imagine a rename of a file with
many hard-links across to a new dir. This problem is harder in a distr file
system if you wish to spread the meta-data. Note that the enforcement happens
automatically with symbolic links. As you point out, with MapR we _could_
implement hard-links within a volume, but chose not to and instead implemented
only symlinks. (I personally find symlinks to be more flexible).
> HDFS hardlink
> -------------
>
> Key: HDFS-3370
> URL: https://issues.apache.org/jira/browse/HDFS-3370
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Hairong Kuang
> Assignee: Liyin Tang
> Attachments: HDFS-HardLink.pdf
>
>
> We'd like to add a new feature hardlink to HDFS that allows harlinked files
> to share data without copying. Currently we will support hardlinking only
> closed files, but it could be extended to unclosed files as well.
> Among many potential use cases of the feature, the following two are
> primarily used in facebook:
> 1. This provides a lightweight way for applications like hbase to create a
> snapshot;
> 2. This also allows an application like Hive to move a table to a different
> directory without breaking current running hive queries.
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