wip

docs/design.md

@@ -44,14 +44,23 @@ flowchart LR
       end
 
       USER -- 1. create/delete RBDPVCBackup --> RPB
-      RBSCM -- 2. take/delete snapshot --> RS
+      RBSCM -- 2. get the target PVC --> RPB
+      RBSCM -- 3. get the PV --> PVC
+      RBSCM -- 4. get the RBD image and pool --> PV
+      RBSCM -- 5. take/delete snapshot --> RS
 
     end
 ```
 
 ### How rbd-backup-system works
 
-TBD
+To take/delete a backup (RBD snapshot), rbd-backup-system works as follows:
+
+1. Create/Delete `RBDPVCBackup` by user.
+2. Get the target PVC from `RBDPVCBackup`.
+3. Get the PV from the target PVC.
+4. Get the RBD image and pool from the PV.
+5. Take/Delete a RBD snapshot for the RBD image.
 
 ### Details