[HDFS-8361] Choose SSD over DISK in block placement

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.8.0, 2.7.1, 3.0.0-alpha1
• Component/s: namenode
• Hadoop Flags: Reviewed
• Assignee: Tsz-wo Sze
• Reporter: Tsz-wo Sze
• Created: 09/May/15 02:58
• Updated: 06/Jan/17 04:31
• Resolved: 16/Jun/15 03:51

Description

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.

public enum StorageType {
  DISK(false),
  SSD(false),
  ARCHIVE(false),
  RAM_DISK(true);

  ...
}

Issue Links

• breaks: HADOOP-12095 org.apache.hadoop.fs.shell.TestCount fails
• is duplicated by: HDFS-9667 StorageType: SSD precede over DISK
• is related to: HBASE-14061 Support CF-level Storage Policy