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https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13490083#comment-13490083
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Jagane Sundar commented on HDFS-2802:
-------------------------------------
First off, I think this is a critical feature for HDFS, and I would like to
thank all of you folks working on this. In order to make snapshots usable to
end users, there is more work to be done in the application software above HDFS
and in the management software. So, getting this feature into HDFS
expeditiously is very important.
Having read the design by Suresh, Nicholas, Sanjay et. al, and the (counter?)
proposal by Aaron, Colin, Todd and Eli - it occurs to me that both designs
share a great deal, and that there are really clever ideas in both proposals.
Acutely aware of the political sensitivity of this JIRA, I want to say only one
thing, hopefully, without offending any of the parties: Considering the amount
of work the layers above have to do, it may be in the best interest of the
Hadoop community to get this feature into HDFS quickly. Given that Suresh,
Nicholas et. al. seem to have working code, and seem much further ahead, it
would serve the HDFS community well if all of us could put our weight behind
that proposal.
And now, on to my real feedback:
1. Having the ability to snapshot sub-directories of the file system, and to
have different snapshot policies for each 'snapshottable' directory is
absolutely essential.
2. In your design document, you state that the administrator needs to configure
a directory as being snapshottable. It would be useful to allow users to be
able to set directories in their own home dir as 'snapshottable'. For example,
the administrator provisions a new user xyzzy and his home directory
/user/xyzzy. xyzzy may then want to create a dir /user/xyzzy/hbase and want to
set it as snapshottable. xyzzy should not have to call the administrator to
make his /home/xyzzy/hbase directory snapshottable. I believe that this was
discussed in the meetup of last week in terms of an ACL. I think this is
important.
Finally, a question:
I still don't understand the 'single client consistency' versus 'multiple
client consistency' issues discussed above. Regardless of how many HDFS client
connections are active on the namenode, a snapshot will capture the HDFS state
at that PIT, right?
> 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: HDFS-2802.20121101.patch,
> HDFS-2802-meeting-minutes-121101.txt, HDFSSnapshotsDesign.pdf, snap.patch,
> snapshot-design.pdf, snapshot-design.tex, snapshot-one-pager.pdf,
> Snapshots20121018.pdf, Snapshots20121030.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 information.
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