Re: Hard to debug NFS loss of connectivity: problem solved

[Emmanuel Florac <eflorac@intellique.com>]

Le Thu, 5 Sep 2013 19:18:00 +0200
Emmanuel Florac <eflorac@intellique.com> écrivait:

> Any hint, idea, etc would be extremely welcome. Even some
> debugging method less painful than digging through huge 
> tcpdumps would be nice :)

I post this answer in the faint hope that it may avoid a long and
painful week of testing to someone else :)

The problem comes from the virtual network adapter "Intel pro 1000"
using the e1000e linux driver. The Intel hardware supports a MTU of
4078 max. On a physical machine, it will fail to set up a greater value
with something like:

# ifconfig eth0 mtu 4079
SIOCSIFMTU: Invalid argument

However the virtual e1000 from VMWare ESX silently accept any value;
then it will mostly work, and fail in mysterious way and only with
certain protocols (such as nfs).

In the case of VMWare virtual machines, using a vmnet3 virtual network
adapter works fine with a mtu of 9000 under NFS. Therefore the problem
is solved.

For the sake of completeness and curiosity, I'll try and see what
happens with a KVM e1000 virtual device.

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