[ovirt-users] Re: Odd question: changing network MTU
Once upon a time, Nir Soffer <nsoffer(a)redhat.com> said:
On Mon, Apr 12, 2021 at 9:05 PM Chris Adams <cma(a)cmadams.net>
wrote:
> What happens if I change the MTU of an active iSCSI network in oVirt? I
> could just go manually change it on each node's iSCSI interfaces, but
> I'm not sure if oVirt might change it back.
oVirt will not modify your setting, the only thing we set on the nodes are
node.startup and node.session.xxx:
Well, it wouldn't be the iSCSI part that I'd worry about, but the
network part. The MTU is set on the networks in oVirt that are used for
iSCSI, not in the iSCSI part of the config.
I actually didn't even realize you could set an MTU in the iSCSI config,
I see it just defaults to 0 (I assume to get interface/path MTU - didn't
see any documentation about the iface.mtu setting). I might look at
that as a method.
If this works and can be useful to others, we can think how to make
this more
generic, maybe adding some configuration that will be applied to all nodes.
Heh, this is such a corner case, I wouldn't really wish doing this on
anyone. :)
> Also, I'm not sure what
> would happen to open iSCSI TCP connections (would they reduce
> gracefully).
Your vms are running on top of multipath, so even if the iscsi
connection was broken and recovered, the vm is protected from
the short outage.
Hmm, true.
What I'm considering right now is not changing anything in oVirt, just
rolling through the systems, setting them to maintenance mode to be
extra safe, manually changing the interface MTUs, and re-activating
them (just need to see if oVirt and/or NetworkManager changes it back
when just going back to active).
--
Chris Adams <cma(a)cmadams.net>