These are the step to add space to and existing Logical Volume on a Volume Group:
1) add disk and perform rescan-scsi-bus.sh
2) Add Physical Volume available for LVM:
pvcreate (-t)* /dev/sdc
3) Exteng the volume group (here namend system) with new create physical volume:
vgextend (-t)* system /dev/sdc
4) Extend target logical volume (here named /dev/system/opt) with new space (here 10gb):
lvextend -L +10G -t /dev/system/opt
5) verify :
lvmdisplay
6) In the end you have to resize physical space :
resize2fs /dev/system/opt
*Always by tiping -t you can test command before execute on production server.