I have been looking for a way to expand my storage capabilities at home while adding in a layer of redundancy to protect my data. Data Robotics offers the DROBO products that seem to be a good fit. What I like most is that I don't have to worry about what RAID level I'm going to be using (I was thinking of doing a raid 5 array) and I can dynamically add/remove drives to add to my storage ability, or replace drives, without taking the array down.
I would LOVE to be able to do this with Linux and a small cheap server. It would likely compare price wise to what Data Robotics is offering with the DROBO line, but would allow me to use ext4 for example to have drive sizes over 2TB (about the size of total storage for which I am looking to start). Data Robotics does not officially support using a drobo on Linux, which is philisophically an issue for me. If they would add support for a linux filesystem that supports sizes > 2TB I would likely stop considering building my own NAS solution and start considering DROBO.