JBOD - just a bunch of disks.
Basically say you have drive 1 and drive 2, JBOD would combine them so it looks like a single drive to the OS. Its used in cases like yours. If one drive fails, you can pull off data from the other drive. (In RAID 0, this isn't possible).
Yes you can have a 3 drive RAID system, and have other drives be different letters, etc. E.g. You can have 1 system drive (C: ), and then a 3 HDD RAID 0 (D: ).
If you have 3 HDD's to spare, you might want to look at RAID 5, which is good for access and security, but you'll lose some of the space to parity.
*edited to make dumb post not have
's instead of : )'s... *