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Date:      Fri, 5 Apr 2002 21:54:43 -0800
From:      Aditya <aditya@grot.org>
To:        Kip Macy <kmacy@netapp.com>
Cc:        freebsd-stable@freebsd.org
Subject:   Re: NFS hang with fxp and Network Appliance fileserver
Message-ID:  <20020406055443.GA82908@mighty.grot.org>
In-Reply-To: <Pine.GSO.4.10.10204052108540.20180-100000@orbit>
References:  <Pine.GSO.4.10.10204052108540.20180-100000@orbit>

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On Fri, Apr 05, 2002 at 09:15:44PM -0800, Kip Macy wrote:
> This sounds like it could be a flow control problem caused by NFS v2's abuse
> of fragmentation/reassembly when using large UDP packets.

I did see a bunch of fragments from the filer when I briefly turned on tcpdump
on that interface whilst it hung.

> What are your mount options? Have you tried v3 with tcp?

I believe mount_nfs under 4-STABLE defaults to v3, udp and netstat bears out
the udp part:

udp4       0      0  192.168.1.37.925       192.168.1.2.2049

here are my current options:

  -r=1024,ro,intr,nodev,nosuid,noauto

I've tried it with and without intr and dumbtimer (there was a post in the
archive that said that turning off the dynamic retransmit timeout estimator
would help for high-performance UDP mounts) but not tcp. As I mentioned, it
works fine on a machine with a de-based NIC without -r=1024.

> Many of our machines in the labs have 8255x based cards and none of them see
> this problem. That is not to say that your problem is not real, just that there
> is some key difference in configuration that we need to isolate.

Okay, I've forced nfs v3 and tcp like this:

  -3,tcp,ro,intr,nodev,nosuid,noauto

and seems to work fine too...so the problem is with fragments on v2 and v3 UDP
mounts (I tested both and they had the same "hanging" behaviour).

Adi

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