Hi Gary.
First, In oVirt 3.6 we will enable editing a few network attributes
while there vms attached to it.
The reason this is forbidden is that until v3.6, by default, vdsm will
recreate the network for
every network edition and this can seriously disturb the network for
the running vms.
Second, if you want to tweak the MTU you should use 'ip link set dev
<dev-name> mtu 9000'
for each device in the network (Bridge, Vlan device, Bond, physical
NIC). Then, you should edit
vdsm persistence json files under both /var/run/vdsm/netconf/<nets/bonds>/
and /var/lib/vdsm/persistence/netconf/<nets/bonds>/. You should find a
file for each network/bond
under those paths.
On the engine DB you should find the proper row in the 'network' table
and update the 'mtu' attribute.
Good luck,

On Thu, Nov 12, 2015 at 4:45 PM, Gary Lloyd <g.ll...@keele.ac.uk> wrote:
> Hi we have upgraded to ovirt 3.5.5 and it seems to have gone well. However
> when we initially configured one of our clusters (back in the day of ovirt
> 3.2) we forgot to adjust two of our vm guest bridges that we use for iscsi
> traffic to an mtu of 9000.
> We have around 50 or so vms using these bridges and we cant change the mtu
> on the data center screen due to the vms being attached to the bridges (This
> message comes up trying to change it).
> We were able to easily override the settings on the hosts in prior versions
> of ovirt (but I don't remember where we did it). Our current 3.4 cluster is
> fine, but I am now setting up a 3.5 cluster with new servers.
> I don't see how changing it to 9000 will cause us any problems due to the
> fact that our older clusters are running those bridges at 9000 anyway.
> Also has anyone experienced the new ui not being as responsive when showing
> the state of vm migrations (doesn't seem to refresh very well on the hosts
> screen).
> Does anyone know if there a way I can force the value to mtu 9000 in the
> database somewhere without blowing it up ?
> Cheers
> Gary Lloyd
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