# Extend logical volume lv_bar to a value of 20G
lvextend -r -L 20G /dev/mapper/vg_foo-lv_bar
# Increase the size of logical volume lv_bar by a value of 200M
lvextend -r -L +200M /dev/mapper/vg_foo-lv_bar
# Extend logical volume lv_bar to utilize 100% of the free extents in volume group vg_foo
lvextend -r -L100%FREE /dev/mapper/vg_foo-lv_bar