Its real simple, I have two servers (lets call them Server A and Server B). Server A acts as an engine and gathers a bunch of information. Would it be better to have Server A update Server B's database, or have Server B connect to Server A's database? In terms of security/efficency.
Which server needs to maintain its security more? That server should contact the other. ... however with databases, replication is often suggested. In this case, since Server A is the main database, Server B would be a slave and receive replication information from Server A.