If you're doing it for the capacity then a separate RAID-0 volume for each disk would be the way to go.
If a disk fails all data on RAID-0 volumes using that disk is lost.
I would still recommend using a redundant volume. If the capacity on a single disk is an issue then with a 4-bay NAS you can get 3x the capacity of a 2 disk NAS, using RAID-5 with 4 disks compared with RAID-1 with 2 disks.