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https://issues.apache.org/jira/browse/HADOOP-1463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12511860
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Hairong Kuang commented on HADOOP-1463:
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Not sure if Raghu's formula is correct. The key is what's the definition of
reserved space. From my understanding dfs.datanode.du.pct and
dfs.datanode.du.reserved are two different ways of specifying reserved space.
dfs.datanode.du.reserved gives an absolute value while dfs.datanode.du.pct
gives a percentage. That's why I said that we need only one of them. Reserved
space is for non-dfs usage including used space for map/reduce.
> dfs should report total size of all the space that dfs is using
> ---------------------------------------------------------------
>
> Key: HADOOP-1463
> URL: https://issues.apache.org/jira/browse/HADOOP-1463
> Project: Hadoop
> Issue Type: Improvement
> Components: dfs
> Affects Versions: 0.12.3
> Reporter: Hairong Kuang
> Assignee: Hairong Kuang
> Fix For: 0.14.0
>
>
> Currently namenode reports two statistics back to the client:
> 1. The total capacity of dfs. This is a sum of all datanode's capacities,
> each of which is calculated by datanode summing all data directories disk
> space.
> 2. The total remaining space of dfs. This is a sum of all datanodes's
> remaining space. Each datanode's remaining space is calculated by using the
> following formula: remaining space = unused space -
> capacity*unusableDiskPercentage - reserved space. So the remaining space
> shows how much space that the dfs can still use, but it does not show the
> size of unused space.
> Each dfs client caculates the total dfs used space by substracting remaining
> space from the total capacity. So the used space does not accurately shows
> the space that dfs is using. However it is a very important number that dfs
> should provide.
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