1. Go to Virtualization
2. Go to Templates
3. Find rhel9-server-small
4. Clone it to a new template, i.e. rhel9-server-small-test
5. In the new template, go to Disks
6. Add a new disk (i.e. blank PVC)

The new Disk added via UI generated this DV in DataVolumeTemplates. Look at the name:

        - metadata:
            name: disk-tan-aardvark-13-clg7hj      <---- this is a static name
          spec:
            storage:
              resources:
                requests:
                  storage: 30Gi
              storageClassName: hostpath-csi-nvme
            preallocation: false
            source:
              blank: {}

7. Now create 2-3 VMs based on this template. In my case the VMs are:

 $ oc get vm | grep rhel9
rhel9-1        91s   Running    True
rhel9-2        70s   Starting   False
rhel9-3        48s   Starting   False

8. Now check the DVs, all 3 VMs have their own DV for the root disk, but there is only one DV for the disk added at step 6.

$ oc get dv
NAME                          PHASE       PROGRESS   RESTARTS   AGE
disk-tan-aardvark-13-clg7hj   Succeeded   100.0%                117s
rhel9-1                       Succeeded   100.0%                117s
rhel9-2                       Succeeded   100.0%                97s
rhel9-3                       Succeeded   100.0%                75s

9. The DV name generated at step 6 does not have the VM {NAME} prefix on it, and therefore the same DV is re-used for every VM cloned from the template, as the DV already exists, they all use the same PVC, skipping provisioning new ones.

The UI should generate a name based on the VM name, like the original template has for the original VM root disk

      dataVolumeTemplates:
        - apiVersion: cdi.kubevirt.io/v1beta1
          kind: DataVolume
          metadata:
            name: '${NAME}'   <----

10. This causes all the VMs to share that 2nd disk, causing problems such as corruption and/or data loss.

11. If I fix the template manually via CLI to look like this, then it works as expected because a new DV object is create for every new VM from template

        - metadata:
            name: ${NAME}-disk-tan-aardvark-13-clg7hj      <--- one DV per VM

Ideally:

• Take this into account when adding Disks to template, its currently dangerous to configure disks of templates via UI.
• Maybe warn/error when a new template tries to creates a DV that already exists, not just re-use it (from backend as well?)