Adding Free Space in NBU Appliance

Hi All,

After adding a new disk shelf to a appliance and assigning the  disks to the appliance , Now i have two pools/volumes one is CATALOG and another is DATA if i add disks to my appliance will my disks automatically goes to a volume/pool or i can have control over it Because i want to add all my disks to my DATA pool and also what is Meta Disk i have read if i add 7 disks 1 disk will be metadisk and only 6 will be actual usable ? 

Thanks,

Nayab