Disks for informix

I might have asked this a while back but cannot find it anywhere I have some filesystems in /dev/vx/rdsk/datadg named as such:- disk1-a-1 disk1-a-7 disk1-b-4 disk2-a-1 disk2-a-7 disk2-b-4 disk1-a-2 disk1-a-8 disk1-b-5 disk2-a-2 disk2-a-8 disk2-b-5 disk1-a-3 disk1-a-9 disk1-b-6 disk2-a-3 disk2-a-9 disk2-b-6 disk1-a-4 disk1-b-1 disk1-b-7 disk2-a-4 disk2-b-1 disk2-b-7 disk1-a-5 disk1-b-2 disk1-b-8 disk2-a-5 disk2-b-2 disk2-b-8 disk1-a-6 disk1-b-3 disk1-b-9 disk2-a-6 disk2-b-3 disk2-b-9 I would like to add one of these to an existing database to give it more space. How do I tell if I need to use an offset??