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https://issues.apache.org/jira/browse/HDFS-15025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17202476#comment-17202476
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Mingliang Liu commented on HDFS-15025:
--------------------------------------

[~ayushtkn] This is good question.

First, I did not see code that depends on the ordinal of the enums, given users 
configure disks with storage name and set the storage policy for directories. 
The existing disk type names and storage polices kept their name and ordinal. 
So I was not thinking this was a "Incompatible" change - even it adds new 
fields ({{isRam}}) to this class. Meanwhile, in the code comment, it says the 
type is sorted by speed, not fixed ordinal.
{code}
@InterfaceStability.Unstable
public enum StorageType {
  // sorted by the speed of the storage types, from fast to slow
{code}

Second, I was not aware of the test failure in multiple previous QA runs of the 
patch (in the pull request). I did not check the last QA run, but would be glad 
if we can find out why this was not reported in PreCommit runs. [~wangyayun] 
Would have a look? I glimpsed and think the test just because it makes 
assumptions about the ordinal. I think your proposal works just fine and fixes 
the test, so +1 on the idea.

CC: [~brahmareddy]

> Applying NVDIMM storage media to HDFS
> -------------------------------------
>
>                 Key: HDFS-15025
>                 URL: https://issues.apache.org/jira/browse/HDFS-15025
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: datanode, hdfs
>            Reporter: YaYun Wang
>            Assignee: YaYun Wang
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 3.4.0
>
>         Attachments: Applying NVDIMM to HDFS.pdf, HDFS-15025.001.patch, 
> HDFS-15025.002.patch, HDFS-15025.003.patch, HDFS-15025.004.patch, 
> HDFS-15025.005.patch, HDFS-15025.006.patch, NVDIMM_patch(WIP).patch
>
>          Time Spent: 12h 10m
>  Remaining Estimate: 0h
>
> The non-volatile memory NVDIMM is faster than SSD, it can be used 
> simultaneously with RAM, DISK, SSD. The data of HDFS stored directly on 
> NVDIMM can not only improves the response rate of HDFS, but also ensure the 
> reliability of the data.



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