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From "zhouyingchao (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-8045) Incorrect calculation of NonDfsUsed and Remaining
Date Thu, 02 Apr 2015 13:29:58 GMT

     [ https://issues.apache.org/jira/browse/HDFS-8045?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

zhouyingchao updated HDFS-8045:
-------------------------------
    Attachment: HDFS-8045-001.patch

Test with "-Dtest=TestSimulatedFSDataset,TestNamenodeCapacityReport,TestFileCreation,TestDecommission"

> Incorrect calculation of NonDfsUsed and Remaining
> -------------------------------------------------
>
>                 Key: HDFS-8045
>                 URL: https://issues.apache.org/jira/browse/HDFS-8045
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>    Affects Versions: 2.6.0
>            Reporter: zhouyingchao
>            Assignee: zhouyingchao
>         Attachments: HDFS-8045-001.patch
>
>
> After reserve some space via the param "dfs.datanode.du.reserved", we noticed that the
namenode usually report NonDfsUsed of Datanodes as 0 even if we write some non-hdfs data to
the volume. After some investigation, we think there is an issue in the calculation of FsVolumeImpl.getAvailable
- following is the explaination.
> For a volume, let's use Raw to represent raw capacity, DfsUsed to represent space consumed
by hdfs blocks, Reserved to represent reservation through "dfs.datanode.du.reserved", RbwReserved
to represent space reservation for rbw blocks, RealNonDfsUsed to represent real value of NonDfsUsed(which
will include non-hdfs files and meta data consumed by local filesystem).
> In current implementation, for a volume, available space will be actually calculated
as  
> {code}
> min{Raw - Reserved - DfsUsed -RbwReserved,  Raw - DfsUsed - RealNonDfsUsed }
> {code}
> Later on, Namenode will calculate NonDfsUsed of the volume as 
> {code}
> Raw - Reserved - DfsUsed - min{Raw - Reserved - DfsUsed - RbwReserved, Raw - DfsUsed
- RealNonDfsUsed}
> {code}
> Given the calculation, finally we will have -
> {code}
> if (Reserved + RbwReserved > RealNonDfsUsed) NonDfsUsed = RbwReserved;
> else NonDfsUsed = RealNonDfsUsed - Reserved;
> {code}
> Either way it is far from the correct value.
> After investigating the implementation, we believe the Reserved and RbwReserved should
be subtract from available in getAvailable since they are actually not available to hdfs in
any sense.  I'll post a patch soon.



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