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https://issues.apache.org/jira/browse/HDFS-1120?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12890975#action_12890975
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Ambikeshwar Raj Merchia commented on HDFS-1120:
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What ever policy is developed, the following should taken into consideration:
The expected life time of the blocks.
My experience oldest data (from creation) is the first to be removed.
Usage of the blocks.
My experience newest data (from creation) is the most like to be read again.
Disk Scrub reads and validates the data. To do the balancing reading and
writing are both necessary. Therefore, should the disk scrub be overloaded to
do the balancing and reduce 50% of the work of balancing?
> Make DataNode's block-to-device placement policy pluggable
> ----------------------------------------------------------
>
> Key: HDFS-1120
> URL: https://issues.apache.org/jira/browse/HDFS-1120
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: data-node
> Reporter: Jeff Hammerbacher
>
> As discussed on the mailing list, as the number of disk drives per server
> increases, it would be useful to allow the DataNode's policy for new block
> placement to grow in sophistication from the current round-robin strategy.
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