Added a disk as jbod and space didn't grow

Hi I have a nsa325 v2 that had a 8tb disk. 

I added another 6tb and wanted to add the space to have 14tb free. The disk appear in the volume together with the other one but space is still under 8tb

Why it didn't grow?? Any way to fix it? Can I remove it and set it as another volume?

Thanks


#NAS_Oct_2019