From: Chris Penney <cpenney@gmail.com>
Subject: Re: NFS Client Performance Question
Date: Wed, 13 Jul 2005 15:57:40 -0400
Message-ID: <111aefd050713125751db40c8@mail.gmail.com>
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On 7/13/05, Peter Staubach <staubach@redhat.com> wrote:
> Chris Penney wrote:
>=20
> >The Itanium page size is 16k (unless I'm mistaken) and the r/wsize is
> >32k so can that still be it?  Or are you saying that it is because the
> >size of the write is only 4k?
> >
>=20
> Well, it is curious that the over the wire WRITE requests are still only =
4K.
> The Sun server is not restricting the transfer sizes, so apparently
> something
> else is.
>=20
> You say that the application on the client is doing random, 4K writes to
> the file?  Is the file opened with O_SYNC or anything special like that?

I'm using a benchmark program (iozone) as it roughly simulations the
real application.  The way I am running it is such that it will
randomly write 4k chunks of the file until the whole file is
rewritten.  So each 4k write should be corrosponding to a specifc
chunk being writen.  What I don't understand is why they are not async
(I'm not an expert at all on NFS).

I reran the test using various chunk sizes and I found that if I use
'-r' to specify 8k or more it always uses async writes.  If I use 6,
4, or 2k I get a lot of fsync writes.  They aren't /always/ fsynced
writes, but most of them are.  I'll see a steam of fsync write, then a
few async, and then back to fsync.

   Chris


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