Those supporting Drobo in this thread only have to look online for numerous instances of problem with Drobo products and their support. That is why I purchased a Synology system years ago. Synology has had time machine support for years. Do yourself a favor before purchasing and compare the two.
Too be fair the people with problems are always going to be louder than the people without any. I've never had any problems in the 6 years of owning drobos. No product is perfect, but if you're happy with what you're using that's all that matters. Oh, and drobos have had time machine support for years as well.