I've been chasing this issue around for a while but can't seem to find the answer.
There are a lot of resources out there describing how to get your Mac to backup to a Sparsebundle on a NAS, and more resources telling you how to write protect the Info.plist file so that Mac OS doesn't resize the image to take up all of your NAS.
However I've got a Drobo connected directly to my Mac Mini. The Drobo pretends to have a 16TB drive so that you can add storage as and when you need it.
I am already using it to back up my MBP over the network to a Sparsebundle and until recently I was using the same scheme (a size limited sparsebundle) to back up the Mac Mini that the Drobo is connected to.
However this has recently stopped working and no matter what I do I still cannot get my Mac to see the Sparsebundle as a TimeMachine aware 'drive'- instead it just backs up to the root of the '16TB' Drobo- and at some point it's going to get rather full.
(And yes, I know that the other solution is to re-partition my Drobo to have a small partition at the start of the disk for Time Machine to use- but it's too late for that as I've already got 1.85TB of data on there and I doubt that I can re-partition that without losing all of the data.)
Can anyone help me get Time Machine to accept my Sparsebundle as a 'disk' that it can backup to?