[jira] Issue Comment Edited: (HADOOP-3637) Support for snapshots

["Sanjay Radia (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-3637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12626371#action_12626371 ] 

sanjay.radia edited comment on HADOOP-3637 at 8/27/08 6:01 PM:
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My comment is regarding the motivation for snapshots as described here.
The introduction of the attached file states that the motivation is timetravel to previous states of the file system.
Clearly HDFS can store data over time and store an evolving state  of some data in different files with name and timestamps. Is this not sufficient? Or are you really looking for a way to look at the complete file system view at particular point in time.
Snapshots in other systems are motivated by recovering accidental deletions or changes.

Also this design proposes snapshotting the entire file system rather then some subtree.
I believe that for backup purposes, one  wants to snapshot different parts of the file system at different degrees of granularity (rather then the filesystem as a whole).  Hence I disagree with the Non-goal of snapshotting subtrees. At the very least the design should be general enough to allow  snapshotting subtrees even though version 1 will implement snapshotting the entire file system. 

      was (Author: sanjay.radia):
    My comment is regarding the motivation for snapshots as described here.
The introduction of the attached file states that the motivation is timetravel to previous states of the file system.
Clearly HDFS can store data over time and store an evolving state  of some data in different files with name and timestamps. Is this not sufficient? Or are you really looking for a way to look at the complete file system view at particular point in time.
Snapshots in other systems are motivated by recovering accidental deletions or changes.

Also this design proposes snapshotting the entire file system rather then some subtree.
I suspect that for backup purposes, one  wants to snapshot different parts of the file system at different degrees of granularity (rather then the filesystem as a whole).
  
> 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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