[Lustre-discuss] Performance Drop creating big files

Kumaran Rajaram krajaram at sgi.com
Fri May 30 14:07:00 PDT 2008


I meant use file-size that are 4x the RAM size :-). So if your RAM size
is 4GB, use atleast 16GB file-sizes for the benchmarks.

On Fri, 2008-05-30 at 15:03 -0600, Lundgren, Andrew wrote:
> Are you suggesting he use machines with 40G of RAM to work with 10G files?
> 
> We have many 800-900G files...  I am not sure that is a realistic number.
> 
> --
> Andrew
> 
> > -----Original Message-----
> > From: lustre-discuss-bounces at lists.lustre.org
> > [mailto:lustre-discuss-bounces at lists.lustre.org] On Behalf Of
> > Kumaran Rajaram
> > Sent: Friday, May 30, 2008 3:01 PM
> > To: Roger Spellman
> > Cc: lustre-discuss at lists.lustre.org
> > Subject: Re: [Lustre-discuss] Performance Drop creating big files
> >
> > Roger,
> >
> > I would suspect the Lustre client side caching influencing your write
> > performance. 10GB is not adequate, try atleast 4x of the RAM size for
> > file-sizes. Try doing the same tests with O_DIRECT flag as it'd truly
> > measure your disk I/O performance bypassing FS + buffer cache.
> >
> > HTH,
> > -Kums
> >
> > On Fri, 2008-05-30 at 16:25 -0400, Roger Spellman wrote:
> > > I am seeing the following odd behavior.  I have several OSSes, each
> > > with a 7T RAID 5.
> > >
> > >
> > >
> > > If I use a single client to create a single 1T file which is striped
> > > to a single OST, the performance starts off at about 400 MB/s (which
> > > is typical for my HW), then gradually decreases, until it
> > reaches 250
> > > MB/s.  I've seen this with both IOZone and dd.
> > >
> > >
> > > As an experiment, I wrote a script that creates two hundred
> > 10G files,
> > > without removing them.  Again, the performance starts off
> > at 400 MB/s.
> > > But, the performance stays nearly the same throughout the test.
> > >
> > >
> > >
> > > The only difference between these tests is that in the second case,
> > > there are lots of opens & closes, and in the first case,
> > just a single
> > > open and close.
> > >
> > >
> > >
> > > Can anyone explain what is happening here, and how to
> > possible fix it?
> > >
> > >
> > >
> > > Thanks.
> > >
> > >
> > >
> > > Roger Spellman
> > >
> > > Sr. Staff Engineer
> > >
> > > Terascala, Inc.
> > >
> > >
> > >
> > >
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> >



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