[ovirt-users] oVirt 4.2 cluster upgrade

I have a 3 node oVirt 4.2.1 cluster, i'm using a self-hosted engine architecture and storage-engine is on a glusterfs replica 3 of the cluster. The oldest CPU is SandyBridge family (E5-2609) and incidentally I have connectivity problems with IPMI NIC of one node, but Hosted Engine HA is enabled and working. Is it safe to upgrade to the last oVirt 4.4 without a down of vm running on the cluster? May I just click on the button Upgrade that appears on the host page?