[jira] Commented: (HADOOP-1463) dfs should report total size of all the space that dfs is using

["Raghu Angadi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-1463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12502000 ] 

Raghu Angadi commented on HADOOP-1463:
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The meaning of "Reserved" that current implements is : "Space that Datanode should try to keep *free* for immediate or future use by either Datanode or some other application". In that sense I think the calculates well. Note that this calculation does not require costly du.

After chatting with Hairong, I think Koji's impression of "Reserved" is : "Disk space that Datanode avoids in its calculations whether it is used or free".  Eg. if there is a partition of 100 GB, 50% is reserved, and DFS occupies 40 GB,  25GB is "available", then "remaining" should be 10GB. This requires equivalent of 'du' for Datanode's data. With the previous interpretation remaining will be zero.

If we want the latter, then we need either do 'du' or maintain disk used, to be sent with every heartbeat.




> 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
>             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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