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Date:	Thu, 27 Dec 2007 06:54:48 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	saeed bishara <saeed.bishara@...il.com>
CC:	linux-kernel@...r.kernel.org, NFS list <linux-nfs@...r.kernel.org>
Subject: Re: read-ahead in NFS server

saeed bishara wrote:
>> (linux-nfs added to cc)
>>
>> I cannot speak for the NFS server code specifically, but 32kb sounds
>> like a network read (or write) data size limit.
> yes
>> Are you using TCP?  Are you using NFSv4, or an older version?
> I'm using NFSv3/UDP.

IMO, you definitely want TCP and NFSv4.  Much better network behavior, 
with some of the silly UDP limits (plus greatly improved caching 
behavior, due to v4 delegations).


> I found that the actual requests size was 16KB, after doing some hacks
> in server&client I managed to make it 60KB, now I see better
> performance, and I see that the average request size is ~130KB which
> means that there is actually read-ahead. but why it's only 130KB? how
> can I make it larger?
> when I run local dd with bs=4K, I can see that the average IO size is
> more than 300KB.

Read-ahead is easier in NFSv4, because the client probably has the file 
delegated locally, and has far less need to constantly revalidate file 
mapping(s).

	Jeff



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