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https://issues.apache.org/jira/browse/HDFS-6482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14054509#comment-14054509
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Suresh Srinivas commented on HDFS-6482:
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Quick comment on the design document part:
{noformat}
Upgrades: We handle DN upgrades by hard linking to the blocks in the previous
directory as before. The only difference with this upgrade is that the new hard
links would be placed into directories in the manner described here. This
shouldn't affect anything, as no code appears to assume that blocks are laid
out in the manner prescribed by LDir.
{noformat}
I think creating hard links with new schema is an issue. The main reason for
hardlinks created as it is done today is to minimize the impact of any bug in
new software. The simplest thing was done where we iterated over directories
and created hardlinks. Rollback must ensure the system goes back to previous
state of the system.
> 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.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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