Feature #45290
openmgr/volumes: Add command to clone a volume from another volume
0%
Description
To provide support for `clone` or `smart cloning` functionality in kubernetes/OCP, we need an interface or functionality which allows
to create a subvolume from an existing subvolume.
Afaict, its not possible to create a volume from an existing volume by a single command/interface, rather the available functionality is the creation of a volume from exising snapshot and not directly from the volume. The workaround/hack would be to achieve this functionality here is creating an intermedia snapshot and then create a volume from the intermediate snapshot , then, upon completion of the new volume creation, delete the intermediate snap. However the smart cloning functionality expects an operation that allows a new volume creation directly from an existing volume.
https://github.com/ceph/ceph-csi/issues/701
Above CSI issue talks about this requirement to support CLONING in ceph CSI project in proper manner.
Updated by Humble Chirammal almost 4 years ago
More details about this clone functionality can be found here:
https://kubernetes.io/docs/concepts/storage/volume-pvc-datasource/
Updated by Humble Chirammal almost 4 years ago
Let me give some more context here:
There are mainly 2 operations to create a new PVC ( empty volume creation is omitted here to avoid confusion).
1) From the snapshot 2) From an existing PVC
In the first case the `dataSource` field in the PVC will be referring to "Snapshot" and in the second case the data source will be referring to an `existing PVC`. The latter is "referred" as CLONE in kube. `A Clone is defined as a duplicate of an existing Kubernetes Volume that can be consumed as any standard Volume would be. The only difference is that upon provisioning, rather than creating a “new” empty Volume, the back end device creates an exact duplicate of the specified Volume.`.
Regarding consistency: There wont be any inflight I/Os on the source PVC, so we are good to take a path of source copy directly to new volume
The data source can be defined in the second case like this:
```
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: clone-of-pvc-1
namespace: myns
spec:
accessModes:
- ReadWriteOnce
storageClassName: cloning
resources:
requests:
storage: 5Gi
dataSource:
kind: PersistentVolumeClaim
name: pvc-1
```
Updated by Kotresh Hiremath Ravishankar almost 4 years ago
Regarding consistency: There wont be any inflight I/Os on the source PVC, so we are good to take a path of source copy directly to new volume
Thanks for this clarification.
Updated by Kotresh Hiremath Ravishankar almost 4 years ago
Humble,
As discussed in [1], it's decided that subvolume clone from another subvolume would not be implemented.
It doesn't makes sense to implement when subvolume creation from snapshot already exists.
Please close this tracker if there are no futher queries
[1] https://docs.google.com/document/d/1YddyUyGkTudPGA3hT3YjeMlvdlP-kqFl0_xwnVHe-88/edit
Thanks,
Kotresh HR