"We wanted a large >= 1TB file server mostly to store backups.
Well I looked at some commercial options and most of them came in at about $20000, and lacked the ability to be easily expanded. The only option to expand a lot of the commercial options was to add another unit and split your data across two of them.
It was the lack of easy expandability that actually won the day.
A lot of the commercial options are very similar to what I build, a lot of them even use the 3ware cards which I was considering.
Well at about this time I noticed an article mentioned Slashdot titled "Build a Terabyte file server for under $5000".