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Date: Fri, 4 May 2012 20:30:48 +0000 (UTC)
From: "Liyin Tang (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-3370) HDFS hardlink
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    [ https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13268685#comment-13268685 ] 

Liyin Tang commented on HDFS-3370:
----------------------------------

<<The main advantage over symbolic links being that when the original link is deleted the 2nd one keeps the actual data from being deleted. Correct>>
Do you mean hard link instead of symbolic links? If the original link deleted, the symbolic link will be broken. But if one of the hard linked files is deleted, other linked files won't be affected.

You are right that the hard link stays on NN only:)

                
> 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-HardLinks.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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