Extending space for raid volume and lvm

hi all
i have hp micro server with 4 disks 2x2 TB and 2x3 TB
I install the nethserver on the 3tb raid 1 partion but the mistake i did was that i didnt use the whole 3 tb i use 2 TB so can i extern the volume ?? the issue the freespace i have is around 980 GB which is not enough to be added to the array of raid in order to extend the space . any idea??
here is the photo of the current HD configuration

i successfully added the space
i first make a new raid 1 for the sdc2 and sdd3 as md3 and then add it to the pv physical volume and then added it to the root volume. the issue was with this commenad:
lvextend -l 100%FREE it wont work
you need to add the space as following
lvextend -l +100%FREE

thank you any way guys


Thanks for the explanation.