I'm keen to find out if we can have 4 servers backing up in pairs of each other. The basic one is that we have one + one = two servers. But I.e. in location 1 we have 2 servers working as Active + Standby for the entire rail way system. While in another location we have another 2 servers - they wait until location 1 loss everything and cut in to take over the entire system in another redundant manner. 

Is it possible ?