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https://issues.apache.org/jira/browse/HADOOP-1463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12508333
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Raghu Angadi commented on HADOOP-1463:
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'df' is very cheap so calculating at every heart beat not bad either.
> Shall we enforce that only one of them is non-zero?
Not necessary depending on calculation of 'remaining space' 'reserved space' in
your equations above. How are those calculated?
According requirements of this jira, this is what I understand the calculation
of available space for datanode is:
{noformat}
remainig space for Datanode =
Min( (dfs.datanode.du.pct * Total_Capacity -
cur_space_used_by_Datanode),
cur_disk_available) - dfs.datanode.du.reserved
{noformat}
cur_disk_available (and total capacity) comes from 'df' and
cur_space_used_by_Datanode is based on 'du'.
The descriptions of these config variables should probably change.
> 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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