I purchased a Drobo (without Droboshare, the add-on network capability, as I've seen reports of it being slow and the price is a bit much for what it does) with the intent of backing up the music and various documents on my Linux box as well as photos and video that I've taken and have on my Mac. It's very quiet and seems to work well, once I worked through various things to get it working on my Gentoo box. It worked fine on my Kubuntu laptop.
Drobo Dashboard, that software that comes with the Drobo, only works on Windows and OS X, so I installed it on my Mac. Drobo Dashboard only allowed formatting in NTFS, HFS+, and FAT32. EXT3 is only an allowable option with Droboshare, The Drobo website does point out Drobo-Utils, the Linux equivalent of the Drobo Dashboard, which does allow formatting in EXT3, so I installed that on my Kubuntu box and formatted the Drobo (I purchased 2 Western Digital 500 GB drives separately) for 2 TB. While it could go higher, the Drobo website mentions a limit of 2 TB, and I did not want to go beyond something that is known to work fine.
From there, I learned about using MacFUSE and fuse-ext2 on OS X to mount EXT3 partitions. I followed those instructions only to find out that the binary mounts the partition as read-only. Writing to the partition is in beta and would require changing a parameter in the source code and compiling it to get that capability. I really did not want to go that direction, so decided to look at formatting Drobo with HFS+.
I had difficulty getting the drive the mount in Gentoo. I already had HFS+ support compiled in the kernel, but found out that I needed to have advanced partition selection, EFI GUID partition support, and support for Large Block Devices enabled in the kernel. 64 bit apparently already has the Large Block Devices support enabled by default. I just had to enable the other two. Things worked fine after that. I plug in the Drobo and KDE finds it just like it does a flash drive. At this time, however, HFS+ support does not work for sizes greater than 2 TB. That's not an issue for me right now.