rbd: add minsnapshotsonimage flag

An rbd image can have a maximum number of
snapshots defined by maxsnapshotsonimage
On the limit is reached the cephcsi will
start flattening the older snapshots and
returns the ABORT error message, The Request
comes after this as to wait till all the
images are flattened (this will increase the
PVC creation time.  Instead of waiting till
the maximum snapshots on an RBD image, we can
have a soft limit, once the limit reached
cephcsi will start flattening the task to
break the chain. With this PVC  creation time
will only be affected when the hard limit
(minsnapshotsonimage) reached.

Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>

charts/ceph-csi-rbd/templates/provisioner-deployment.yaml

@@ -133,6 +133,7 @@ spec:
             - "--rbdhardmaxclonedepth={{ .Values.provisioner.hardMaxCloneDepth }}"
             - "--rbdsoftmaxclonedepth={{ .Values.provisioner.softMaxCloneDepth }}"
             - "--maxsnapshotsonimage={{ .Values.provisioner.maxSnapshotsOnImage }}"
+            - "--minsnapshotsonimage={{ .Values.provisioner.minSnapshotsOnImage }}"
             {{- if .Values.provisioner.skipForceFlatten }}
             - "--skipforceflatten={{ .Values.provisioner.skipForceFlatten }}"
             {{- end }}

charts/ceph-csi-rbd/values.yaml

@@ -120,6 +120,8 @@ provisioner:
   softMaxCloneDepth: 4
   # Maximum number of snapshots allowed on rbd image without flattening
   maxSnapshotsOnImage: 450
+  # Minimum number of snapshots allowed on rbd image to trigger flattening
+  minSnapshotsOnImage: 250
   # skip image flattening if kernel support mapping of rbd images
   # which has the deep-flatten feature
   # skipForceFlatten: false