Xen users - Oct 2008 - NFS-server in DOM-0. something to avoid?

Hi all,

One of my hypervisors (XEN-3.2.1, openSUSE_11.0) is acting as
NFS-server, not only for DOM-U''s, but also for other nfs-clients on my
lan.
If one of the DOM-U''s is doing quite some network-IO I found that the
hypervisor often freezes, and once in a while even generates OOPses.
All of the NFS-clients then complain about the NFS-server not
reachable...

I posted this in SuSE''s bugzilla, and got the reply that one should run
as little as possible services in the hypervisor, specially not NFS
As the xen-configfiles and xen-images are stored within the area
exported by NFS, is it not possible to NFS-export it by a DOM-U.


Any comments?

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On Tue, Oct 28, 2008 at 10:42 AM,  <J.Witvliet@mindef.nl>
wrote:
> I posted this in SuSE''s bugzilla, and got the reply that one
should run as
> little as possible services in the hypervisor, specially not NFS
just nitpicking: you don''t run NFS in the hypervisor.  it runs in the
Linux kernel that runs as a privileged guest: Dom0.  incidentally, the
subject line is more accurate :-)


-- 
Javier

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>> As the xen-configfiles and xen-images are stored within the area
exported
by NFS, is it not possible to NFS-export it by a DOM-U.

On Tue, Oct 28, 2008 at 9:21 AM, Javier Guerra <javier@guerrag.com> wrote:
> On Tue, Oct 28, 2008 at 10:42 AM,  <J.Witvliet@mindef.nl> wrote:
> > I posted this in SuSE''s bugzilla, and got the reply that one
should run
> as
> > little as possible services in the hypervisor, specially not NFS
>
What''s the reasoning behind exporting the xen config files and images?
Yes
generally you don''t want anything on the Dom0 that you don''t
necessarily
need including file sharing.

Grant McWilliams

Some people, when confronted with a problem, think "I know, I''ll
use
Windows."
Now they have two problems.


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From: xen-users-bounces@lists.xensource.com
[mailto:xen-users-bounces@lists.xensource.com] On Behalf Of Grant
McWilliams
Sent: Tuesday, October 28, 2008 5:33 PM
To: Javier Guerra
Cc: Witvliet, J., CDC/IVENT/OPS/I&S/PLS/SMP/HRM/RP1;
xen-users@lists.xensource.com
Subject: Re: [Xen-users] NFS-server in DOM-0. something to avoid?




>> As the xen-configfiles and xen-images are stored within the area
exported by NFS, is it not possible to NFS-export it by a DOM-U.


On Tue, Oct 28, 2008 at 9:21 AM, Javier Guerra <javier@guerrag.com>
wrote:


	On Tue, Oct 28, 2008 at 10:42 AM,  <J.Witvliet@mindef.nl> wrote:
	> I posted this in SuSE''s bugzilla, and got the reply that one
should run as
	> little as possible services in the hypervisor, specially not
NFS
	


What''s the reasoning behind exporting the xen config files and images?
Yes generally you don''t want anything on the Dom0 that you
don''t
necessarily need including file sharing. 

 
We have one larger machine, 6*300GB disks, 8GB mem, 4 xeons acting as
NFS-server and some smaller machines with only 36GB disks.
All the (smaller) machines mount /srv/xen, so i can start clients where
ever i want...
Other parts hold a copy of gwdg.de, and one of the DOM-U''s is an
installation-server
The machine used to be non-xen, but i thought it was a waste of
resources not to use the machine to the most
 

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>
>
> What''s the reasoning behind exporting the xen config files and
images? Yes
> generally you don''t want anything on the Dom0 that you
don''t necessarily
> need including file sharing.
>
> We have one larger machine, 6*300GB disks, 8GB mem, 4 xeons acting as
> NFS-server and some smaller machines with only 36GB disks.
> All the (smaller) machines mount /srv/xen, so i can start clients where
> ever i want...
> Other parts hold a copy of gwdg.de, and one of the DOM-U''s is an
> installation-server
> The machine used to be non-xen, but i thought it was a waste of resources
> not to use the machine to the most
>
> ------------------------------
>
Then I assume these smaller machines are real computers that are pulling the
xen disk image from across the network? I''ll also assume that each of
the
smaller machines are also Xen enabled and have more than one DomU (otherwise
why all the fuss?)?

If so this doesn''t seem very optimal. If I were you I''d slim
down the Dom0
to bare nothing, set up the 6*300GB disks in some sort of RAID (I assume
that this is already the case), make it a logical volume (LVM) and give the
Volume to the first DomU (the nfs server). The rest of the DomUs can come up
off Xen images on the Dom0 OS drive or they could come off the nfs share
from the first DomU just like the little machines on the network. This
get''s
your Dom0 back to what it''s supposed to be doing - staring DomUs. If
you
have any other services being served by Dom0 I''d also get them
virtualized.

Grant McWilliams


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