Xen users - Oct 2008 - NFS between domU and dom0 causes the virtual network to freeze! Please help

Hello,

I''m a new user to Xen, so please be patient with me.
I just installed a dom0 on my root-server and I also got a xenU to work with 
routed network. I can access from both sides and I can access both machines 
from any other computer too.
So far - so good.. (gentoo on both ends by the way)

My plan was to use a mounted NFS-directory from dom0 on my domU to place /home 
(and later other directories too) physically on the dom0 (for easy backups 
running from the dom0). I think this is a typically setup from a xen 
environment.

Well, the mount of the exported nfs-directory on my domU works well. I can do 
a listing, I can touch a file and I even can copy a small testfile (several 
100k) over the NFS. But when I try to copy a larger File (several MBs) the 
network to my domU freezes! The domU isn''t reachable any more. Neither
from
dom0 nor from any other computer. 
The dom0 is working normal - I can reach all the places and can ping anywhere. 
Only domU is affected. It seems that the virtual network of xen is crashed. 
The OS itself of the domU isnt affected as I can just use the xen-console to 
attach to the domU. There I can''t see any strange things - only the
network
isn''t working any more.
Furthermore I can''t restart my domU. It seems that xen can''t
attach the vif1.0
Interface the the domU any more. My only chance is a complete reset of the 
whole dom0 (restarting)!
It seems that this problem have something to do with NFS as I can copy larger 
files (several 100MBs) using netcat. This don''t break anything. It must
have
something to do with nfs.
Are there any information I can provide for more details about this problem? 
Are there any known bugs about nfs over xen? What can I do to collect more 
debugging informations to get ideas where the problem maybe resides? Can this 
have something to do with wsize or rsize of the nfs protocol?

Any help would be really appreciated as I urgently need to get this machine to 
work with all its domUs!

With best Regards,
Martin Fernau

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I need to mention that I currently have xen 3.3 and xen-tools 3.3 installed 
with kernel 2.6.21-xen on gentoo (both dom0 and domU have gentoo installed 
and both use the same kernel version).

Am Donnerstag, 16. Oktober 2008 schrieb Martin Fernau:
> Hello,
>
> I''m a new user to Xen, so please be patient with me.
> I just installed a dom0 on my root-server and I also got a xenU to work
> with routed network. I can access from both sides and I can access both
> machines from any other computer too.
> So far - so good.. (gentoo on both ends by the way)
>
> My plan was to use a mounted NFS-directory from dom0 on my domU to place
> /home (and later other directories too) physically on the dom0 (for easy
> backups running from the dom0). I think this is a typically setup from a
> xen environment.
>
> Well, the mount of the exported nfs-directory on my domU works well. I can
> do a listing, I can touch a file and I even can copy a small testfile
> (several 100k) over the NFS. But when I try to copy a larger File (several
> MBs) the network to my domU freezes! The domU isn''t reachable any
more.
> Neither from dom0 nor from any other computer.
> The dom0 is working normal - I can reach all the places and can ping
> anywhere. Only domU is affected. It seems that the virtual network of xen
> is crashed. The OS itself of the domU isnt affected as I can just use the
> xen-console to attach to the domU. There I can''t see any strange
things -
> only the network isn''t working any more.
> Furthermore I can''t restart my domU. It seems that xen
can''t attach the
> vif1.0 Interface the the domU any more. My only chance is a complete reset
> of the whole dom0 (restarting)!
> It seems that this problem have something to do with NFS as I can copy
> larger files (several 100MBs) using netcat. This don''t break
anything. It
> must have something to do with nfs.
> Are there any information I can provide for more details about this
> problem? Are there any known bugs about nfs over xen? What can I do to
> collect more debugging informations to get ideas where the problem maybe
> resides? Can this have something to do with wsize or rsize of the nfs
> protocol?
>
> Any help would be really appreciated as I urgently need to get this machine
> to work with all its domUs!
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Okay, it seems that rsize and wsize is the cause for my problems. I manually 
set both to 1024 for testing purposes and now I can dd a large file of >500MB
over NFS.
How can I determine the best settings for both values?

Regards,
Martin Fernau

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2008/10/16 Martin Fernau <m.fernau@cps-net.de>:
> Okay, it seems that rsize and wsize is the cause for my problems. I
manually
> set both to 1024 for testing purposes and now I can dd a large file of
>500MB
> over NFS.
> How can I determine the best settings for both values?
>
> Regards,
> Martin Fernau
>
Try with 8192, with NFSv3 you can even try 16384 and 32768. You can
evaluate the performance with time+dd on the mounted NFS share...

Regards,
Ciro

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