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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3637) Support for snapshots
Date Thu, 28 Aug 2008 01:14:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12626398#action_12626398
] 

Allen Wittenauer commented on HADOOP-3637:
------------------------------------------

A few folks have asked me to clarify my position on what I really want to be able to do with
snapshots.

A solution that provides a single snap of the entire file system is acceptable for the short
term. For the medium term, the solution should provide multiple snaps of the entire file system
and have them all usable simultaneously.  But ultimately, I want to be able to snapshot directories
(partial file systems) multiple times a day and have all of those snapshots available.  [a
la ZFS' .zfs and NetApp's .snapshot system ]  Different file paths have different priorities
with regards to a desired level of recover-ability. 

I think Sanjay is correct in that snapshots will get used more for the "oops!" situations
than a full blown recovery.  As an end user of other snapshot systems, it is extremely nice
being able to compare/contrast multiple versions of the same file.  This would be especially
prevalent in the FUSE and NFS proxy cases, I'd imagine, where the fs is running around in
a POSIX-like costume.

I don't want to understate the need to be able to do a full file system recovery though. 
Having to bring the system down just to take a snapshot is annoying.  

I want to be able to do both as they provide different solutions for different needs.  Any
solution that prevents fulfilling what I need over the long haul, to me, is probably not a
good idea.  I haven't dug into the spec to see if that is the situation here.  

*plink* *plink*

> Support for snapshots
> ---------------------
>
>                 Key: HADOOP-3637
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3637
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: Snapshots.pdf, Snapshots.pdf
>
>
> Support HDFS snapshots. It should support creating snapshots without shutting down the
file system. Snapshot creation should be lightweight and a typical system should be able to
support a few thousands concurrent snapshots. There should be a way to surface (i.e. mount)
a few of these snapshots simultaneously.

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