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https://issues.apache.org/jira/browse/HDFS-6482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14053895#comment-14053895
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Suresh Srinivas commented on HDFS-6482:
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HDFS-5535 added support for rolling upgrade. During that time, given datanode
layout rarely changes, rollback was not considered for datanodes. Given that
this jira is changing datanode layout version, impact on rollback should be
considered before this change can be committed.
> 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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