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Re: XFS perfomance degradation on growing filesystem size

To: xfs@xxxxxxxxxxx
Subject: Re: XFS perfomance degradation on growing filesystem size
From: Jens Beyer <jens.beyer@xxxxxxxx>
Date: Mon, 7 Jul 2008 10:04:09 +0200
In-reply-to: <20080704075941.GP16257@xxxxxxxxxxxxxxxxxxxxx>
References: <20080704064126.GA14847@xxxxxxxx> <20080704075941.GP16257@xxxxxxxxxxxxxxxxxxxxx>
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User-agent: Mutt/1.5.17+20080114 (2008-01-14)
On Fri, Jul 04, 2008 at 12:59:41AM -0700, Dave Chinner wrote:
> On Fri, Jul 04, 2008 at 08:41:26AM +0200, Jens Beyer wrote:
> > 
> > I have encountered a strange performance problem during some 
> > hardware evaluation tests: 
> > 
> > I am running a benchmark to measure especially random read/write 
> > I/O on an raid device and found that (under some circumstances) 
> > the performance of Random Read I/O is inverse proportional to the 
> > size of the tested XFS filesystem. 
> > 
> > In numbers this means that on a 100GB partition I get a throughput 
> > of ~25 MB/s and on the same hardware at 1TB FS size only 18 MB/s 
> > (and at 2+ TB like 14 MB/s) (absolute values depend on options, 
> > kernel version and are for random read i/o at 8k test block size).
> Of course - as the filesystem size grows, so does the amount of
> each disk in use so the average seek distance increases and hence
> read I/Os take longer.

But then - why does the rate of ext3 does not decrease and stays at the
higher value? 


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