OK, so I know the answer to this question is probably "it depends..." but we have a number of legacy M5000 servers with only 256G RAM. One has 5 zones with a total mcap of 220G for the zones, leaving 36G for the global zones. They all have at least one Oracle 12 database running, and one has a number of other intense applications running to do with geolocation. This zone has 72G assigned to it.
One of these zones was recently created to migrate a Solaris 10 zone to 11.3. What we have found is that when this zone is started the global zone (and eventually some of the non
global zones as well) becomes inaccessible via ssh, although you can run "ssh global <command>" and that typically works. Also we cannot get Solaris access via the console (it just hangs). We tried shutting the temporary zone down with "ssh global zoneadm -z temp-zone halt". The zone never completes shutdown, "ssh global zoneadm list -cv" showing it as "shutting down". We will probably have to crash the server to regain access.
Is there a recommended minimum value for global zone memory, or some formula to come up with a safe value.