Assume you have an oVirt cluster with hundreds of VM networks. Now you add a
new host to the cluster. In order for it to move to the Operational state,
it must have all required networks attached to it. The easiest way to do it is
to attach networks to a label, and then place that label on a NIC of the added
host. However, if there are too many networks, Engine could fail to setup them
all at once. This is caused by a slow VDSM setupNetworks call that is not able
to finish within the 180 seconds long vdsTimeout of Engine.

VDSM performance changes would be included in ovirt-4.2, currently in

Initscripts performance patch is targeted for EL 7.5.

The following table shows maximal number of networks that can be handled within
the vdsTimeout. The measured setupNetworks command handles one network with
static IP and N VLAN+bridge networks with no IP. Edit covered a move of all
networks from one NIC to another.

Please note that given numbers are for reference only.

installed N add edit del
ovirt-4.2 190 180s 127s 67s
ovirt-4.2 and patched initscripts 350 138s 176s 89s
ovirt-4.1 150 179s 164s 93s
ovirt-4.1 and patched initscripts 215 111s 172s 79s

The best improvement could be achieved with the initiscripts patch. It is
not distributed in repositories yet, but you can apply it manually without much
effort. However, even with bare ovirt-4.2 there is a significant speed-up.