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https://issues.apache.org/jira/browse/HDFS-3370?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13396466#comment-13396466
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M. C. Srivas commented on HDFS-3370:
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The fact that HBase wants to use hard-links for backup does not make the backup
itself safe. Backup itself only becomes safe if HDFS (not HBase) promises to
never modify a file once it is closed. Otherwise, a process that accidentally
writes into the hard-linked file will corrupt "both" copies. Simple having
HBase say "oh, but we never modify this file via HBase" is not strong enough.
The backup has to be absolutely immutable.
So the use-case here requires a commitment from HDFS to never be able to either
append or ever write into an existing file. So it means no chance of
random-write or NFS support.
> 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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