Guys and Gals.
I'm using my Drobo as TM Drive.
It's automatically formatted as a 2TB drive, no matter how many disks you have in there. I have currently 2x 750GB in there, which gives me an effective capacity of 750.
Now, after exactly 5 days of Leopard and TM, the thing is full (give or take 50GB). Drobo tells me that and asks me to insert an additional drive. BUT, OSX thinks there's still some 1.3TB free, because of the 2TB formatting thing. So, TM won't start deleting stuff, although the drive is full. That sucks.
Torsten