add some alternate ideas

Author: Mayank Kumar

contributors/design-proposals/storage/pv-to-rbd-mapping.md

@@ -18,7 +18,8 @@ We want to make RBD image name generation more deterministic, so that in catastr
 situations, we can derive the PVC name from rbd image name/metadata and allow customer
 the following options:
 - Backup RBD volume data for specific customers and hand them their copy before deleting 
-  the RBD volume.
+  the RBD volume. Without knowing from rbd image , which customers they belong to we 
+  cannot do this.
 - Create PV with the given RBD name and pre-bind it to the desired PVC so that customer
   can get its data back.
 
@@ -29,11 +30,10 @@ was no way to restore customer data. This proposal aims to store pvc name as met
 RBD image name so that in catostrophic scenarios, the mapping can be restored by just looking
 at the RBD's.
 
-## Implementation
+## Proposal
 
 ### Implementation Detail
 
-
 #### Current Implementation
 
 ```go
@@ -58,14 +58,23 @@ func (r *rbdVolumeProvisioner) Provision() (*v1.PersistentVolume, error) {
 
  // create RBD Image name 
  image := fmt.Sprintf("kubernetes-dynamic-pvc-%s", uuid.NewUUID())
+
+ // Create a base64 encoding of the PVC Name
  rbdImageName := b64.StdEncoding.EncodeToString([]byte(r.options.PVC.Name))
+
+ // Append the base64 encoding to the string `kubernetes-dynamic-pvc-`
  rbdImageName = fmt.Sprintf("kubernetes-dynamic-pvc-%s", rbdImageName)
  r.rbdMounter.Image = rbdImageName
 ```
 
 #### API Changes
 There are no API changes needed for this work
 
+## Alternative Proposals
+- Append the fully qualified PVC name(namespace-pvcname) to the string
+  - This exposes the customer name directly to Ceph Admins
+- Use SHA1 hash for rbd names
+  - The hashes are one way so we cant use them to get back the pvc name
 
 ### Misc
 - Document how Pre-Binding of PV to PVC works in dynamic provisioning