OK ;-)
3 node HCI 2+1 data/arbiter
added 3 compute-only nodes via host install without HE support which add no storage to the
gluster (install still adds them as peers).
With 2 compute-only nodes inactive/down I updated the third compute node (no contributing
bricks) and saw all VMs pausing and glusterd on the HCI nodes "lost quorum on brick
engine/vmstore/data" when it rebooted to activate the new kernel.
Had to launch additional compute-only node to let glusterd on HCI nodes recover quorum.
Seems glusterd computes quorum based on total peers (6) not on redundancy (2+1).
With the gluster volumes down, running VMs remain paused according th virsh, HE and UI
aren't there, hosted-engine --vm-status reports "not retrieved from storage"