This policy tries to put files onto devices which are on different networks, if that isn't possible then devices on the same network are returned as "desperate" options.
We aim to have as many copies as we can on unique networks, if there are 2 copies on one network and none on another, with a min of 2, we will still over-replicate to the other network. When called from the rebalancer we will therefore rebalance across networks and reduce the correct copy.
By default we class 2 hosts as being on 2 different networks if they're are on different /16 networks (255.255.0.0). This can be controlled using server settings, with a list of network "zones", and then a definition of a netmask for each "zone".
mogadm settings set network_zones location1,location2 mogadm settings set zone_location1 192.168.0.0/24 mogadm settings set zone_location2 10.0.0.0/24
Zone names and netmasks must each be unique.