I run the unRaid NAS and swear by it. I am using Hitachi 2TB 7200 RPM drives in a RM enclosure that will take 12 hot swap drives. The unRaid NAS uses the reiserFS under slackware Linux and maintians a single parity drive Data is not striped so a two drive failure does not destroy the array.

unRaid (Slackware 13.1) does run Squeezeserver although I have not yet put it up but several have. It is not a trivial process but I understand it does work.

It supported by a very active forum similar to this one with some very smart Linux people on it. The unRaid architecture, runs from a flash drive but can be disk based. addons are prevelant and the entire system is maintained through a web based interface so a non linux person can deal with it quite easily.

It supports a concept called user shares where a share will be spread across selected drives so you can just deal with "\music" and not care where the files are although when you write them to the drive you still have the option of selecting a specific drive or letting unraid do it algorithmically.