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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2802) Support for RW/RO snapshots in HDFS
Date Wed, 31 Oct 2012 21:05:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13488234#comment-13488234

Suresh Srinivas commented on HDFS-2802:

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,
> 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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