[Lustre-discuss] Performance Drop creating big files

[Lundgren, Andrew]

I get it.

Thanks!

> -----Original Message-----
> From: Kumaran Rajaram [mailto:krajaram at sgi.com]
> Sent: Friday, May 30, 2008 3:07 PM
> To: Lundgren, Andrew
> Cc: Roger Spellman; lustre-discuss at lists.lustre.org
> Subject: RE: [Lustre-discuss] Performance Drop creating big files
>
>
> 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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