A friend of mine got a Drobo and ended up returning it because he felt it was unreliable. Dunno whether that was a fluke.

I've got two LaCie two-disk RAID gizmos that have Firewire and they've been pretty good to me over the past year that I've been using them -- one for all my bulk storage needs and the other as a TimeMachine backup. I never really notice the fan noise, although I do notice the noise of the disks spinning up when I sit down to use the computer. (Particularly since I'll type something like 'ls' and will need to wait ten seconds before the disk can respond.)