1. Unown all the disks on both nodes in maintenance mode
2. "Clean configuration and intialize all disks" on both nodes
3. Remove the ownership of the data partition from the second node
Example: # storage disk removeowner -disk 1.1.16 -data true
4. Assign the ownership of all data partition to the first node
Example: # storage disk assign -disk 1.1.16 -owner node1 -data true
5. Create your big aggr as desired
For the removal and assignment of the partitions you have to be at least in advanced mode.