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https://issues.apache.org/jira/browse/HDFS-8361?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14584385#comment-14584385
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Tsz Wo Nicholas Sze commented on HDFS-8361:
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Joe, thanks for looking at the patch and the comments. Will fix the typo and
add a new test.
> Eventually, storage types might be characterized by more than one dimension,
> so a single ordering may not serve the purposes of all placement policies.
Let's deal with multiple dimensional characteristic when there is a need.
> Choose SSD over DISK in block placement
> ---------------------------------------
>
> Key: HDFS-8361
> URL: https://issues.apache.org/jira/browse/HDFS-8361
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Tsz Wo Nicholas Sze
> Attachments: h8361_20150508.patch, h8361_20150612.patch
>
>
> BlockPlacementPolicyDefault chooses the StorageType by iterating the given
> StorageType EnumMap in its natural order (the order in which the enum
> constants are declared). So DISK will be chosen over SSD in One-SSD policy
> since DISK is declared before SSD as shown below. We should choose SSD first.
> {code}
> public enum StorageType {
> DISK(false),
> SSD(false),
> ARCHIVE(false),
> RAM_DISK(true);
> ...
> }
> {code}
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