Why would you want all of the replicas to be able to fail over and become master?
A common pattern is to separate writes from reads. Writes go to a small pool, reads get replicated into everywhere. Your read-only replicas will only ever be slaves, and do not need persistence.
A common pattern is to separate writes from reads. Writes go to a small pool, reads get replicated into everywhere. Your read-only replicas will only ever be slaves, and do not need persistence.