On Tue, Apr 13, 2021 at 3:03 AM Chris Adams <c...@cmadams.net> wrote:
> Once upon a time, Nir Soffer <nsof...@redhat.com> said: > > On Mon, Apr 12, 2021 at 9:05 PM Chris Adams <c...@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). > That is generally a bad idea, oVirt has its own network persistence, it would be reverted on reboot and the engine would complain that those networks are out of sync. So the safest way is to change MTU in the engine and then sync all networks on all hosts that have this network attached. > -- > Chris Adams <c...@cmadams.net> > > Best regards, Ales -- Ales Musil Software Engineer - RHV Network Red Hat EMEA <https://www.redhat.com> amu...@redhat.com IM: amusil <https://red.ht/sig>
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