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https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13396769#comment-13396769
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Daryn Sharp commented on HDFS-3370:
-----------------------------------
I understand hardlinks likely aren't meant to be. However I'd like to point
out:
* Hardlinks cannot be implemented at a library level. The n-many directory
entries must be able to reference the same inode, which unlike symlinks, are
not bound by the permissions used to access any other of the paths to the
hardlink. Filesystem support is required.
* Hardlinks shouldn't rule out the possibility of random-write (not suggesting
it, it was brought up earlier). There may need to be some changes to the lease
manager to apply the lease to the underlying inode instead of path.
* Hardlinks for backup aren't sufficient except by convention. That's where
snapshots using hardlinks+COW blocks is interesting. COW blocks also open the
door to zero-write copies.
> 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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