If you're building a file server, the capacity and performance benefits you will get from doing a RAID-0 (striping only) with any number of disks will not be worthwhile, as what will happen is one of the disks will die and all of your data will be gone.

If you can afford it, a mirrored pair of bigger disks would be far better.

Also, a device like the drobo or a readynas or a computer installed with a self-maintaining filesystem like opensolaris/solaris11express with ZFS will do sort of an in-software RAID 5 that's purported to work very well.

Although for anybody on a budget, two drives mirrored will probably be the best thing, or striping but with an automatic backup to another drive, nightly.