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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2802) Support for RW/RO snapshots in HDFS
Date Mon, 05 Nov 2012 21:26:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13490938#comment-13490938
] 

Tsz Wo (Nicholas), SZE commented on HDFS-2802:
----------------------------------------------

> ... (a) snapshot creation time and memory usage should be O(1), ...

Eli, the memory usage in ATM's proposal is not O(1) since it adds tags for every INode, therefore,
it is O(N), where N is the number of INodes.  It is much worse that the additional memory
usage is required even if the snapshot feature is not used.  You are right that ATM's design
attempt to solve such problems but I believe the attempt fails.
                
> 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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