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Date: Wed, 16 May 2012 03:30:23 +0000 (UTC)
From: "Sanjay Radia (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=13276415#comment-13276415 ] 

Sanjay Radia commented on HDFS-3370:
------------------------------------

* I see the additional complexity in quotas because HDFS quotas are directory based (like several file systems). I think this is addressable if we double count the quotas along both path. 
* Permissions are not a problem since the file retains the file permissions and both paths to the file offer their own permissions.
* I don't understand Srivas's rename example.
Srivas, in MapR I suspect that renames are only allowed within a volume and such hard links would be supported only within a volume. Can you explain the problem with some more details.
                
> 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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