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https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13487972#comment-13487972
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Suresh Srinivas commented on HDFS-2802:
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[~shv]Thanks for your comments. Some answers here:
versions seem like an interesting capability to support. I want to think about
it more. However snapshots have their own use cases as well. Ability to
snapshot and attach a name to it comes handy for writing applications using
this functionality.
.snapshot is a convention that is used widely and requires no changes to many
of the APIs such as rm, ls etc. In fact we had initially proposed using
.snap_<snapshot_name>. After looking at many other file systems, where
.snapshot convention is used to identify the snapshot, we decided to go with it.
bq. Creating duplicate INodes with a diff, this is sort of COW technique,
right? Sounds hard.
Hopefully this should not add too much code complexity. But this is being done
to avoid taking too much memory for snapshots on the namenode.
bq. My dumb question: can I create a snapshot of a subdirectory that is a part
of a snapshot above it?
This is not a dumb question :-) The design already supports nested snapshots. I
will add an update to the document describing this.
> 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, 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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