There's an inordinate amount of players enjoying Diablo 2 from Emily's blog

One of the main issues outlined by the team is the way D2R Items players' personal data and characters are stored. If you've played an Activision or Blizzard multiplayer game over the past few years it's likely that players typically login to servers that are closest to your place of residence as you can. It'sn't an individual server per se however, it's a group of servers that serve an entire area.

In the end, all of these servers have their own regional databases that contain the information of the characters playing on them. This is necessary because there's an inordinate amount of players enjoying Diablo 2 to just continually upload everyone's data to a only one central point.

"Most of your actions in game are executed against this regional database as it's more efficient, and your character's 'locked and locked to keep the integrity of the individual record of your character. The global database also comes with backup in the event that the main database fails."

The regional databases are periodically able to send information back into the central database which means that Blizzard has a singular record (with backups) of your D2R Ladder Items Level 88 Barbarians, Necromancers , and others. All sounds good until the central database gets overwhelmed and the entire system, just like the engineers that work on it, is in need of a break.