Identify the LUN to extend on DS8000, and update the size: chfbvol -cap <new_size_GB> <LUN_ID>
dscli> chfbvol -cap 100 -quiet 5125
On the target host, check if the LUN size has increased, else wait 30s, and try again:
# bootinfo -s hdisk0
Or
# getconf DISK_SIZE /dev/hdisk0
Update the VG size, also possible on rootvg, but not on LUN containing an active paging space (you can do it by moving paging on another disk during this operation):