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https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13488234#comment-13488234
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Suresh Srinivas commented on HDFS-2802:
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bq. Can you send a link?
NetApp uses this - search on google, you will find many other file systems such
as HP X9000 File System etc.
bq. My concern is that you have a directory dr with two subdirectories sd2 and
sd3. You create a snapshot of sd2 and sd3 under the same name. Then create a
snapshot of dr with the same name. What happens?
The design should work fine. Every snapshot has the following:
- A directory where the snapshot is created
- A name that is unique for a given directory where snapshot is taken
- Internally snapshot dir + name is mapped to a unique snapshot ID and the
diffs are maintained against that snapshot ID.
When snapshot is accessed, the path used provides snapshotted directory and
snapshot name. It gets mapped to a unique snapshot ID. For this we can get to
snapshotted version.
> 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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