Re: reducing imaxpct on linux

From: Michael Monnerie <michael.monnerie@is.it-management.at>
To: "CZEH, Istvan" <iczeh@virusbuster.hu>
Cc: xfs@oss.sgi.com
Subject: Re: reducing imaxpct on linux
Date: Fri, 12 Nov 2010 16:18:08 +0100	[thread overview]
Message-ID: <201011121618.09040@zmi.at> (raw)
In-Reply-To: <1289571841.20961.44.camel@sekli>

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On Freitag, 12. November 2010 CZEH, Istvan wrote:
> I already made the things written in the FAQ (question 32.) but still
> having the problem. Maybe I should find the oldest data again? It
> won't be easy...

I guess the FAQ is a bit wrong here:

http://xfs.org/index.php/XFS_FAQ#Q:_Why_do_I_receive_No_space_left_on_device_after_xfs_growfs.3F

Because it is not the "oldest" data, but the data that is within the 
space in the first TeraByte of the partition.

Dave Chinner explained to me, that XFS will split data equally amongst 
all AGs. So if you have a partition with 4TB and 4 AGs, and you put 1TB 
data on that partition, each AG will have around 250GB data, meaining 
you still have 750GB free within the first TB.
When you do NOT use the inode64 option, all inodes will be placed in the 
first TB *only*. Even when later you use the inode64 option, it might 
not succeed in finding space for the inodes.

I can imaginge this would help
1) Run xfs_fsr, if it finds files below 1TB and defrags them to a space 
>1TB, you're lucky
2) use the "noikeep" option before doing what XFS Q32 describes. If you 
remove a large portion of inodes, and later move them back, they should 
be newly allocated, and when you use inode64 then, chances are good the 
go at a place >1TB.
3) Find files that are placed at <1TB. I think some xfs_db magic can do 
that, but I never used it so someone else should say.

Anyway: Dave, I'd like to "repair" the FAQ question 32 to be more 
correct and descriptive, would my description be correct?

-- 
mit freundlichen Grüssen,
Michael Monnerie, Ing. BSc

it-management Internet Services: Protéger
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