I've been very happy with FreeNAS running on a recycled PowerEdge 400SC. I boot it off a USB thumbdrive and it manages to spin up and down the six SATA drives I'm using with even even with a cheapie 4-port PCI SATA card.
My workload is pretty light though as it hosts media and I only stream it from two devices max at a time.
But it's hard to beat the price and comprehensive protocol support. FTP, Samba, NFS, AFP, Time Machine backups, iTunes sharing, etc.
I did the same with openfiler, has worked well for about 4+ years. It has 4x400GB in RAID5 which gives 1.2TB of storage.
I've been planning an upgrade to 4x2TB for a 6TB RAID, but I haven't had the time or the $ for the upgrade.
I used some of the storage space as a time machine destination, but Apple has issues with Time Machine over SMB, and it got to the point where it was too slow, so I bought an USB disk and just back-up to that.
But have you thought of the power costs for running that machine? That's why I in addition to protocol and other feature support, I also look at power consumption. These things will most likely be running 24/7/365 and the energy costs add up over time.
My workload is pretty light though as it hosts media and I only stream it from two devices max at a time.
But it's hard to beat the price and comprehensive protocol support. FTP, Samba, NFS, AFP, Time Machine backups, iTunes sharing, etc.
http://www.freenas.org/