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https://issues.apache.org/jira/browse/HADOOP-1463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12577174#action_12577174
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Hairong Kuang commented on HADOOP-1463:
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This jira is closed. Please open a new jira if you think there is a bug.
Reserved space is considered in the first statement when calculating remaining.
The reserved space is for non-dfs usage including map/reduce, other
applications, and unusable disk space on a partition etc. Only when non-dfs
usage is more than the reserved space, remaining is set to be the the available
space on the disk.
> dfs.datanode.du.reserved semantics being violated
> -------------------------------------------------
>
> Key: HADOOP-1463
> URL: https://issues.apache.org/jira/browse/HADOOP-1463
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.15.3, 0.16.0
> Reporter: Hairong Kuang
> Assignee: Hairong Kuang
> Priority: Blocker
> Fix For: 0.15.0
>
> Attachments: usedSpace.patch, usedSpace.patch
>
>
> 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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