partitioning with disk utility question

here's my setup:

one, dual bay enclosure (1.5TB x2):
OWC Mercury Elite - AL Pro Dual Bay Enclosure
https://eshop.macsales.com/item/Other World Computing/MEFW934AL2/

and one, two pack of 1.5TB Seagate HD
http://accessories.us.dell.com/sna/...=CJ&cid=24471&lid=566643&acd=10550055-683153-

Total: paid $310 including shipping for the 3.0TB external setup.

I'm going to use FW400(since my MB pro has no 800 port) and partition this into two 1.5TB partitions. one for storage, and one for time machine backup
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My question is if i choose 2 partitions in disk utility, will it automatically know to use one of the 1.5TB Seagate HD for one partition and the other 1.5TB seagate for the 2nd partition? or will it use half of one and half the other?

I would like one partition to be one seagate 1.5TB HD, and the 2nd partition to be the other, that way if one fails i have a backup (using Time Machine with one partition to backup the other 1.5TB drive).

just want to make sure i'm not missing a setting somewhere in disk utility..

 

i don't believe I striped the drives RAID-0 (because i don't know what that is haha). How can I know for sure? I don't want it to evenly write the data across both HD's.. I want one 1.5TB drive for storage and the other 1.5TB unit for backup of the previous 1.5TB storage drive.

I have them installed into a dual bay enclosure and hooked up via 1 firewire 400 cable to the comp. I made 2 partitions with disk utility, so i mounts as 2 drives (1.5TB each). Is this setup correct? or is it setup RAID-0 or whatever evenly distributes the data between both drives?