I recently came accross unRAID which is a storage server based on Linux.
Big upside for the product is it allows a cheap old system to be built using different sized hard drives while still using a recoverable option using a parity drive. Data is not stripped accross drives so if the system died for some reason the drives can be placed in another system and accessed easily. Also runs off a USB stick so frees up another drive.
Without going into details the site is www.lime-technology.com