[jira] [Created] (HDFS-8361) Choose SSD over DISK in block placement

["Tsz Wo Nicholas Sze (JIRA)" <ji...@apache.org>]

Tsz Wo Nicholas Sze created HDFS-8361:
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             Summary: 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


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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