[OpenAFS] Weird issue with AFS hang on a couple of legacy RHEL 6 servers

[Jeffrey E Altman]

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On 9/8/2020 1:31 PM, Sebby, Brian A. (sebby@anl.gov) wrote:
> Hi,
>=20
> I have a few legacy RHEL 6 servers that are still running an older 1.6.=
x
> series DKMS client, which were recently patched and rebooted.=C2=A0 On =
a
> couple of them, access to AFS is now just hanging =E2=80=93 and I canno=
t figure
> out why.=C2=A0 They have the same kernel release and kernel module as s=
ome
> other systems on the same network that are working, so it doesn=E2=80=99=
t look
> like it would be any sort of firewall issue.=C2=A0 Would anyone have an=
y
> suggestions on how to debug this?=C2=A0 I don=E2=80=99t know if I can u=
pgrade them to
> 1.8 since we are trying to keep our legacy systems fairly static.

I debugged one of the problem systems.  The issue would not be fixed by
any newer version of OpenAFS.  The underlying problem is related to the
computation of the rx interface MTU when the host has a network
interface with an MTU smaller than the minimum jumbo packet size.  The
work around is "afsd -rxmaxmtu <N>" where

  N =3D <network-mtu> - 56

It should be noted that unlike the OpenAFS servers and the Windows
client, the UNIX cache manager does not disable jumbo by default.

Jeffrey Altman
AuriStor, Inc.

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email;internet:jaltman@auristor.com
title:CEO
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