Extend Hard Disks into SC4020

Hi Folks,

I have explored articles around of adding new Hard Disks into Storage Array and have seen the guide from community. 

One of my customer had two Disk folder as attached and he bought new Hard Disks and want to expand volumes. Total of 7 New Drives. 

My concern is that can we add Unassigned Disk into separate Disk Folders. ( Like 4 Disks to Disk Folders 1 and 3 Disk to another ). 
I have attached current usage on these. I am looking forward your suggestions on it. 

Thank for your time. 

Best Regards,

Myat