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https://issues.apache.org/jira/browse/HDFS-6482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14081365#comment-14081365
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Suresh Srinivas commented on HDFS-6482:
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[~cmccabe], does this patch change the directory structure and during rollback
the new directory structure is retained? If so, this is a concern for me and I
am -0 on this. We should at least make sure we have rollback tests to check
that things work and there are no undocumented hidden assumption in the older
software version (to which we are rolling back to) is broken. Given rollback
could be to any older release from where upgrade to this version is allowed;
that makes testing and ensuring nothing is broken that much more hard.
> 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: 6482-design.doc, 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-6482.8.patch, HDFS-6482.9.patch, HDFS-6482.patch,
> hadoop-24-datanode-dir.tgz
>
>
> 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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