Drobo's are good for backup storage, not for video editing. While the 5D does claim to be capable of photo/video editing according to their website, I've never known Drobo to build boxes for fast storage for editing/vfx. They are great at cheap backup storage though, easily expandable, and simple to setup. However, I don't think I would want to edit consistently off of one.
Promise, Lacie, Small Tree, Active Storage, etc are where I'd put my video files if I'm working in Smoke....especially if your business has client supervised sessions. You can't afford to skimp on storage if you're going to have the client sitting over your shoulder. If you're just looking to learn Smoke or work on personal projects, then you can take your own chances!