Re: XFS perfomance degradation on growing filesystem size

[Jens Beyer <jens.beyer@1und1.de>]

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? 

Thanks,
Jens