[GitHub] [hadoop] LeonGao91 commented on a change in pull request #2288: HDFS-15548. Allow configuring DISK/ARCHIVE storage types on same device mount

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LeonGao91 commented on a change in pull request #2288:
URL: https://github.com/apache/hadoop/pull/2288#discussion_r514875357



##########
File path: hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
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@@ -1503,6 +1503,20 @@
   public static final boolean DFS_PROTECTED_SUBDIRECTORIES_ENABLE_DEFAULT =
       false;
 
+  public static final String DFS_DATANODE_ALLOW_SAME_DISK_TIERING =
+      "dfs.datanode.same-disk-tiering.enabled";
+  public static final boolean DFS_DATANODE_ALLOW_SAME_DISK_TIERING_DEFAULT =
+      false;
+
+  // HDFS-15548 to allow DISK/ARCHIVE configured on the same disk mount.
+  // Beware that capacity usage might be >100% if there are already
+  // data blocks exist and the configured ratio is small, which will
+  // prevent the volume from taking new blocks until capacity is balanced out.
+  public static final String DFS_DATANODE_RESERVE_FOR_ARCHIVE_PERCENTAGE =

Review comment:
       The intention is to have a configuration as a "default value" for all disks, as in normal cases one datanode server comes with the same type of HDDs. Therefore we can keep the DN configuration less verbose for most of the use cases.
   
   However, you are right that we should allow users to configure different values, and it is a good idea to put it under "dfs.datanode.data.dir".
   I will create a follow-up JIRA to address it, so we can keep this PR from being too big, as that could involve quite a bit of change.




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