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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HDFS-2802) Support for RW/RO snapshots in HDFS
Date Sat, 20 Oct 2012 16:36:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13480772#comment-13480772
] 

Suresh Srinivas edited comment on HDFS-2802 at 10/20/12 4:34 PM:
-----------------------------------------------------------------

bq. In fact I think the design is based my comment on HDFS-3960
Actually that is not true. We have been mulling over many of these ideas for a long time.
HDFS-3960 was just create to get the discussion going.

The design we are proposing is to let DNs send the length. The length known is what goes into
the snapshot instead of recording either zero length for block under construction or having
to initiate communication with datanodes/implicitly getting it from DN. From what I have heard
from some HBase folks 5-10 seconds lagging should be workable for them. That is why I want
to to talk to few HBase folks in the design review. 
                
      was (Author: sureshms):
    bq. In fact I think the design is based my comment on HDFS-3960
Actually we have been mulling over some of these ideas for a long time. HDFS-3960 was just
started to get the discussion going.

The design we are proposing is to let DNs send the length. The length known is what goes into
the snapshot instead of recording either zero length for block under construction or having
to initiate communication with datanodes/implicitly getting it from DN. From what I have heard
from some HBase folks 5-10 seconds lagging should be workable for them. That is why I want
to to talk to few HBase folks in the design review. 
                  
> 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: 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
information.

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