Comment Re:why is the system not master / master or slave (Score 3, Interesting) 82
there is physical distance between main and backup site. that means there are physical limitations how fast transaction can be done if you require master/master configuration (you are limited by speed of signal propagation).
to ensure both sides to have same data (sync replication) you need 2x time distance. that means high latency.
and stock exchange wants to have low latency as much as possible. so only design is to have main / DR (DR being async copy).