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https://issues.apache.org/jira/browse/HDFS-14313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16900515#comment-16900515
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Lisheng Sun commented on HDFS-14313:
------------------------------------

Thanx  [~linyiqun] for your deep review. I updated this patch as your 
comments. 

checkstyle issue:
{code:java}
./hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/FSCachingGetSpaceUsed.java:64:
    public Builder setBpid(String bpid) {:35: 'bpid' hides a field. 
[HiddenField]
{code}
I think it is not a problem. I haved uploaded the v11 patch. Could you help 
review it?  Thank you. 

> Get hdfs used space from FsDatasetImpl#volumeMap#ReplicaInfo in memory  
> instead of df/du
> ----------------------------------------------------------------------------------------
>
>                 Key: HDFS-14313
>                 URL: https://issues.apache.org/jira/browse/HDFS-14313
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode, performance
>    Affects Versions: 2.6.0, 2.7.0, 2.8.0, 2.9.0, 3.0.0, 3.1.0
>            Reporter: Lisheng Sun
>            Assignee: Lisheng Sun
>            Priority: Major
>         Attachments: HDFS-14313.000.patch, HDFS-14313.001.patch, 
> HDFS-14313.002.patch, HDFS-14313.003.patch, HDFS-14313.004.patch, 
> HDFS-14313.005.patch, HDFS-14313.006.patch, HDFS-14313.007.patch, 
> HDFS-14313.008.patch, HDFS-14313.009.patch, HDFS-14313.010.patch, 
> HDFS-14313.011.patch
>
>
> There are two ways of DU/DF getting used space that are insufficient.
>  #  Running DU across lots of disks is very expensive and running all of the 
> processes at the same time creates a noticeable IO spike.
>  #  Running DF is inaccurate when the disk sharing by multiple datanode or 
> other servers.
>  Getting hdfs used space from  FsDatasetImpl#volumeMap#ReplicaInfos in memory 
> is very small and accurate. 



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