Who knows just what they are synching between the data centers, but it was announced several times in the Lodestone that they were having a lot of trouble with it, and it was denying players access. Maybe it's DF related, or account authentication when zoning. But it was causing issues with stability for the service.
Edit:
Found this post from a few weeks ago in the Lodestone:
http://na.finalfantasyxiv.com/lodest...682b20b31f9e6c
For whatever reason, they need the two data centers to have a reliable connection. And it's not just the Data Centers, but the Clients as well. The JP servers are still needed in the background for all of us (look at your connections in netstat or resmon, and you'll see your client opens a line to a server in JP even though you are playing on a server in NA).[Recovery] Notice of Network Recovery (Oct. 22)
During the following time, we were experiencing instability with our network connections, which caused instability with connections from North American and European regions to the Japanese data center and vice versa.
We are pleased to announce that the issue has been resolved. We apologize for any inconvenience.
[Date & Time]
From Oct. 21, 2013 1:30 p.m. to Oct. 22, 2013 3:15 a.m. (PDT)
[Details]
- Instability with connections from North American and European regions to the Japanese data center
- Instability with connections from Japan to the North American/European data center
[Cause]
- Internet instability
[Affected Service]
- FINAL FANTASY XIV: A Realm Reborn