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https://issues.apache.org/jira/browse/HDFS-15025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17202757#comment-17202757
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Mingliang Liu commented on HDFS-15025:
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[~wangyayun] Thanks for taking a look!

The topic is not only about the test failure, which can be fixed either way. 
The more important question is about compatibility since FSImage may depend on 
the ordinal and hence existing data can not work with this patch. It seems even 
more concerning if it fails silently by parsing existing storage types wrongly. 
To fix it, we first need to keep the existing ordinal by moving NVDIMM to the 
end and updating the comment. Secondly we need to make sure adding isRAM does 
not break compatibility either. I assume it does not but it would be great if 
we can confirm. That’s why I suggested we need to (manual) test more about this 
for compatibility.

> 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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