Hi Murlio, Thanks for that. Yes, iSCSI Target is configured with ACL Yes, all the Gateways have the same amount of sessions. Yes, I followed your 6 step-suggestion. So what happened is - and I won't go into all the boring details of how, why, and how - I discovered the remains of another iSCSI Target on the 2nd Gateway. Installing and using tergetcli I removed this old target, which allowed me to then remove and then re-attach the 2nd Gateway to the "real" target (using the Ceph GUI - resetting the gateways to be identical once again), and then ran through the 6-steps. I now have all three oVirt Hosts logged into all three Ceph iSCSI Gateways, with each of the four LUNs reporting connectivity to all three Gateways, etc. So that's the Gateways-connectivity issue resolved. However, I still have the other issue: I still come up with the "The following LUNs are already in use..." message and I still have the same results - ie log messages re: connectivity issues with the new (iSCSI) Storage domain briefly appearing and then being removed again (see 1st post in this thread). This happens with all four LUNs no matter which of the three Gateways I point oVirt Admin GUI at. (Yes, I tried this twelve times to cover the twelve possible combinations). So, anyone got any further ideas? :-) Cheers Dulux-Oz