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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2802) Support for RW/RO snapshots in HDFS
Date Mon, 22 Oct 2012 21:50:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13481840#comment-13481840

Aaron T. Myers commented on HDFS-2802:

bq. That is the goal.

Great, I'm glad you agree. I'd be happy to personally work on a more time/space efficient
snapshot solution.

bq. Where I disagree is with the assertion that we cannot get to it starting with a simple
implementation. I would like to get the simple implementation done ASAP with all the tests
developed in parallel. Then we will change the implementation for better efficiency both in
time and space. Tests will help ensure the correctness of optimizations.

I suspect you'll find that implementing the copying solution will not be much easier than
a zero-copy/COW solution, and so seems to me like implementing the copying solution will result
in a lot of wasted development/testing work.

To be completely clear, if it makes sense to implement a copying solution as an interim development
stage, then that's fine, but I don't think that a solution which copies all of the files/directories
that are being snapshotted should be merged to trunk.
> Support for RW/RO snapshots in HDFS
> -----------------------------------
>                 Key: HDFS-2802
>                 URL: https://issues.apache.org/jira/browse/HDFS-2802
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: data-node, name-node
>            Reporter: Hari Mankude
>            Assignee: Hari Mankude
>         Attachments: snap.patch, snapshot-one-pager.pdf, Snapshots20121018.pdf
> Snapshots are point in time images of parts of the filesystem or the entire filesystem.
Snapshots can be a read-only or a read-write point in time copy of the filesystem. There are
several use cases for snapshots in HDFS. I will post a detailed write-up soon with with more

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