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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6482) Use block ID-based block layout on datanodes
Date Mon, 07 Jul 2014 18:48:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14054008#comment-14054008
] 

Colin Patrick McCabe commented on HDFS-6482:
--------------------------------------------

The new "current" directory will contain hardlinks to the block and metadata files in the
"previous" directory.  So it seems like rollback should work fine in this case.

It would be nice to add a unit test where we upgrade a DataNode from the non-blockid-based
version to a blockid-based version, and then do a rollback.  Can you add this, James?  Since
you already added {{hadoop-24-datanode-dir.tgz}}, it shouldn't be too difficult to add a unit
test that rolls back to this version from the new version.

> Use block ID-based block layout on datanodes
> --------------------------------------------
>
>                 Key: HDFS-6482
>                 URL: https://issues.apache.org/jira/browse/HDFS-6482
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.5.0
>            Reporter: James Thomas
>            Assignee: James Thomas
>         Attachments: HDFS-6482.1.patch, HDFS-6482.2.patch, HDFS-6482.3.patch, HDFS-6482.4.patch,
HDFS-6482.5.patch, HDFS-6482.6.patch, HDFS-6482.7.patch, HDFS-6482.patch
>
>
> Right now blocks are placed into directories that are split into many subdirectories
when capacity is reached. Instead we can use a block's ID to determine the path it should
go in. This eliminates the need for the LDir data structure that facilitates the splitting
of directories when they reach capacity as well as fields in ReplicaInfo that keep track of
a replica's location.
> An extension of the work in HDFS-3290.



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