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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, 29 Oct 2012 17:28:17 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13486173#comment-13486173

Aaron T. Myers commented on HDFS-2802:

bq. Many of the things you are repeating again, about space and creation efficiency etc. I
have addressed them in many comments. Please do not comment as if the current work is not
considering it. 

I definitely didn't mean to beat a dead horse on this subject. My apologies that the comment
came across that way. I was trying to enumerate the differences between the documents, and
propose a specific solution to this problem. I certainly didn't intend to imply that the current
work is not considering this problem, hence why I referenced HDFS-4125 in my comment.

bq. Our solutions will be based on well known solution in the literature for this problem.
Please see on HDFS-4125.

I have been following HDFS-4125, but the comment in HDFS-4125 regarding the solution you're
referring to wasn't posted until after my most recent comment.

bq. Some of the differences around administrative can be made configurable, if need be. These
are surround aspect of the feature.

Sounds good.

bq. Given repeated feedback about optimizations we are working on updating the implementation
and design. Earlier the goal was to get the inefficient but correct first implementation with
tests and have design review, followed by optimization. Given the feedback so far, we will
post updated design next week. Possibly hold a design review in around two weeks.

Cool. I look forward to reading the updated design doc.

bq. BTW if this design/implementation needs changes later we can have a discussion. At this
point in time, I would like to focus on getting parts of the implementation we have had in
our prototype out in this branch. I am fine if we need to throw away parts of it.

My preference would be to collaborate on and agree to a design upfront so that we can come
up with something that will be amenable to everyone before we spend a lot of time implementing
something and potentially discarding it.

By the way, I forgot to mention that the design document I posted contains some discussion
and specific design proposals regarding the consistency of NN/DN data in snapshots. Please
take a look at that as well.
> 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: HDFSSnapshotsDesign.pdf, 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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