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From "Pete Wyckoff (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2991) dfs.du.reserved not honored in 0.15/16 (regression from 0.14+patch for 2549)
Date Tue, 11 Mar 2008 18:24:46 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12577546#action_12577546
] 

Pete Wyckoff commented on HADOOP-2991:
--------------------------------------


Can we just first look at fixing DF.getCapacity() - leave it if you like, but add a method
DF.getTotalUsableSpace() which returns DF.getUsed() + DF.getAvailable(). And stop using DF.getCapacity()
!

And in the meantime, Joy, I think it does make some sense to poll users and see (a) who even
knows about the new semantics and (b) who thinks they are useful and (c) who thinks they are
usable.

--- pete
 
ps the example would be really, really helpful.

ps again Hairong, all your comments apply only if the setting for reserved = Everything (including
completely unusable by ANYBODY space that cannot be used on the drive + all other space over
the lifetime of the drive and machine).


> dfs.du.reserved not honored in 0.15/16 (regression from 0.14+patch for 2549)
> ----------------------------------------------------------------------------
>
>                 Key: HADOOP-2991
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2991
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.15.0, 0.15.1, 0.15.2, 0.15.3, 0.16.0
>            Reporter: Joydeep Sen Sarma
>            Priority: Critical
>
> changes for https://issues.apache.org/jira/browse/HADOOP-1463
> have caused a regression. earlier:
> - we could set dfs.du.reserve to 1G and be *sure* that 1G would not be used.
> now this is no longer true. I am quoting Pete Wyckoff's example:
> <example>
> Let's look at an example. 100 GB disk and /usr using 45 GB and dfs using 50 GBs now
> Df -kh shows:
> Capacity = 100 GB
> Available = 1 GB (remember ~4 GB chopped out for metadata and stuff)
> Used = 95 GBs   
> remaining = 100 GB - 50 GB - 1GB = 49 GB 
> Min(remaining, available) = 1 GB
> 98% of which is usable for DFS apparently - 
> So, we're at the limit, but are free to use 98% of the remaining 1GB.
> </example>
> this is broke. based on the discussion on 1463 - it seems like the notion of 'capacity'
as being the first field of 'df' is problematic. For example - here's what our df output looks
like:
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda3             130G  123G   49M 100% /
> as u can see - 'Size' is a misnomer - that much space is not available. Rather the actual
usable space is 123G+49M ~ 123G. (not entirely sure what the discrepancy is due to - but have
heard this may be due to space reserved for file system metadata). Because of this discrepancy
- we end up in a situation where file system is out of space.

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