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Koji Noguchi commented on HADOOP1463:

> From my understanding dfs.datanode.du.pct and dfs.datanode.du.reserved are two different
ways of specifying reserved space.
>
I used to think the same. But there shouldn't be two config variables that serve the same
purpose.
So, assuming "dfs.datanode.du.reserved" is the one for "space reserved for nondfs usage *whether
it is used or unused*"
I'd want
{noformat}
MIN( Total_Capacity  cur_space_used_by_Datanode  dfs.datanode.du.reserved, cur_disk_available)
{noformat}
I'm not sure where "dfs.datanode.du.pct" should fit. Maybe
{noformat}
MIN( Total_Capacity  cur_space_used_by_Datanode  dfs.datanode.du.reserved, cur_disk_available)
* dfs.datanode.du.pct
{noformat}
> dfs should report total size of all the space that dfs is using
> 
>
> Key: HADOOP1463
> URL: https://issues.apache.org/jira/browse/HADOOP1463
> 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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