My main beef with Drobo is the way the file system works. You specify a faux file size of the drive that Mac OS recognizes, but it doesn't relate to the actual file size of the drives.
It turns out you should make this faux file size as large as you can (16TB) as the faux file size restricts the actual file size, so I made my faux file size 2TB and now actually have 2.5TB of storage, to make my drobo recognize it I have to reformat all the disks and lose the data. Daft.