Hi Spirit,
thanks for the valuable suggestion,
this way the Dell cluster results seem much improved:
--- pve8.xxx.yyy ping statistics ---
15921298 packets transmitted, 15921294 received, 2.51236e-05% packet loss, time 595912ms
rtt min/avg/max/mdev = 0.016/0.029/7.526/0.034 ms, ipg/ewma...