Introduce enhancement for mapping OVA disks

docs/enhancements/multidisk-ova.md

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+---
+title: multidisk-ova
+authors:
+  - "@mansam"
+reviewers:
+  - "@mnecas"
+approvers:
+  - "@mnecas"
+creation-date: 2024-11-26
+last-updated: 2024-11-26
+status: implementable
+---
+
+# Storage Mapping for multi-disk OVA Imports
+
+## Release Signoff Checklist
+
+- [ ] Enhancement is `implementable`
+- [ ] Design details are appropriately documented from clear requirements
+- [ ] Test plan is defined
+- [ ] User-facing documentation is created
+
+## Summary
+
+In the current release of Forklift it is possible to import OVA appliances
+that have been exported from a vSphere environment.  However, all of
+an appliance's disks are mapped to the same storage class, and it is
+not possible for the end user to indicate that certain disks should be
+mapped differently from others. In order to support more use cases, it
+should be possible to select map a destination storage class for each
+disk of an OVA appliance individually. Forklift does not normally allow
+such fine-grained storage mapping because it becomes untenable with a
+large number of VMs, but because an OVA plan is expected to involve only
+a small number of VMs it should be acceptable.
+
+### Example StorageMap
+
+```yaml
+spec:
+  map:
+    - destination:
+        storageClass: fast
+      source:
+        id: vm1-disk1
+    - destination:
+        storageClass: slow
+      source:
+        id: vm1-disk2
+    - destination:
+        storageClass: fast
+      source:
+        id: vm2-disk1
+    - destination:
+        storageClass: default
+      source:
+        id: default
+  provider:
+    destination:
+      name: host
+      namespace: default
+    source:
+      name: ova
+      namespace: default
+```
+
+### Goals
+
+* Forklift will enable end users to individually map each disk of a
+  vSphere OVA appliance to a destination storage class of their choice.
+
+### Non-Goals
+
+* Forklift will not allow fine-grained storage mapping for any VM
+  providers other than OVA.
+
+## Proposal
+
+The OVA inventory adapter should be modified to surface each disk from
+each OVA appliance as its own source storage class. The OVA VM builder
+would then be modified to respect these mappings when building the
+DataVolumes rather than assuming only a single mapping.
+
+### Security, Risks, and Mitigations
+
+No new security risks are introduced by permitting disks to be mapped
+individually.
+
+## Design Details
+
+### Test Plan
+
+Existing tests for the OVA provider should be updated to include
+individual disk mappings. No additional tests should be necessary.
+
+### Upgrade / Downgrade Strategy
+
+Permitting OVA disks to be mapped individually does not require any
+changes to the update or downgrade path of Forklift itself, although
+Plans created with this feature would not be compatible with a downgraded
+version of Forklift as the previous version would not recognize the individual
+disk mappings.
+
+### Open Questions
+
+Should we continue, to support a default mapping or require each disk to
+be specifically mapped?  Allowing a default would preserve the current
+ease of use for simple cases, but may make it easier to make mistakes
+since plan validation would not be able to ensure that each of the disks
+had been mapped as desired.
+
+## Implementation History
+
+* 11/26/2024 - Enhancement submitted.