RAID1 (LaCie) Partition possible?

Hello everyone,

I recently purchased a LaCie 4TB (2TBx2TB) 2Big Thunderbolt drive for the dual purposes of creating and storing a "bootable backup" of my hard drive on my iMac and for exernal storage of all my family's media files (photos, music, videos). Is it possible and advisable to partition this RAID1 setup??
According to SuperDuper! backup literature they STRONGLY recommend that any backup be partitioned or on a separate disk all together from other regular storage (photos, music...).
Each time I go to partition my mirrored RAID set using DiskUtility it states in the partition info that "this partition can't be modified. Changing a RAID partition may leave the set unusable."

The LaCie 2Big does not support JBOD. Do I have any resolution?? I should mention that I do have Time Machine running daily backups, although from what I've read..theses are not "bootable backups", more for recovering individual files.

Any and All Help is MUCH APPRECIATED as I'd like to have some sort of decent backup in place ASAP.
Thank You!
Marcelo