Howto replace a failed LVM raid1/mirror disk for an active volume

Issue

• How to replace a failed LVM raid1/mirror disk leg without inactivating the Logical Volume (LV). This is required for system volumes like /root and /swap.
• r1vg/r1lv has a lost disk leg but it is active and open and it must stay active and open.

# lvs -a r1vg 
  Couldn't find device with uuid 5drE0Q-jqiU-H17g-eEVZ-XAlO-40AL-8qVmMh.
  WARNING: Couldn't find all devices for LV r1vg/r1lv_rmeta_1 while checking used and assumed devices.
  WARNING: Couldn't find all devices for LV r1vg/r1lv_rimage_1 while checking used and assumed devices.
  LV              VG   Attr       LSize    Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  r1lv            r1vg rwi-aor-p- 1016.00m                                    100.00          
  [r1lv_rimage_0] r1vg iwi-aor--- 1016.00m                                                    
  [r1lv_rimage_1] r1vg iwi-aor-p- 1016.00m                                                    
  [r1lv_rmeta_0]  r1vg ewi-aor---    4.00m                                                    
  [r1lv_rmeta_1]  r1vg ewi-aor-p-    4.00m