YaYun-Wang commented on a change in pull request #2189:
URL: https://github.com/apache/hadoop/pull/2189#discussion_r477304478



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File path: 
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsVolumeSpi.java
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@@ -77,6 +77,9 @@
   /** Returns true if the volume is NOT backed by persistent storage. */
   boolean isTransientStorage();

Review comment:
       The "isTransientStorage" method is still available. 
   In the original code, “isTransient“ and “isTransientStorage” methods are 
used to determine whether to suport FsDatasetCache, Persistent, Quota, and 
Movable. FsDatasetCache will be used When the storage type is persistent. 
NVDIMM is RAM to some extent, which is fast. However, NVDIMM is a persistent 
storage type.  Then, "isTransient" and "isTransientStorage" used to determine 
whether to support FsDatasetCache can't meet the requirements. Therefore, we 
add "isRAM" and "isRAMStorage" methods to decide whether cache is supported or 
not. And the other functions, such as, Persistent,  Quota, and Movable judged 
by " isTransient" and "isTransientStorage" methods.




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