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Humble Chirammal 134e11e26e doc: correct PVC expansion documentation

Signed-off-by: Humble Chirammal <hchiramm@redhat.com>

2020-06-16 10:31:29 +00:00

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Dynamically Expand Volume

Dynamically Expand Volume
- Prerequisite
  - Expand RBD PVCs
    - Expand RBD Filesystem PVC
    - Expand RBD Block PVC
  - Expand CephFS PVC
    - Expand CephFS Filesystem PVC

Prerequisite

For filesystem expansion to be supported for your kubernetes cluster, the kubernetes version running in your cluster should be >= v1.15 and for block volume expand support the kubernetes version should be >=1.16. Also, ExpandCSIVolumes feature gate has to be enabled for the volume expand functionality to work.
The controlling StorageClass must have allowVolumeExpansion set to true.

Expand RBD PVCs

Expand RBD Filesystem PVC

pvc.yaml

apiVersion: v1
items:
- apiVersion: v1
  kind: PersistentVolumeClaim
  metadata:
    annotations:
      pv.kubernetes.io/bind-completed: "yes"
      pv.kubernetes.io/bound-by-controller: "yes"
      volume.beta.kubernetes.io/storage-provisioner: rbd.csi.ceph.com
    creationTimestamp: "2019-12-19T05:44:45Z"
    finalizers:
    - kubernetes.io/pvc-protection
    name: rbd-pvc
    namespace: default
    resourceVersion: "3557"
    selfLink: /api/v1/namespaces/default/persistentvolumeclaims/rbd-pvc
    uid: efe688d6-a420-4041-900e-c5e19fd73ebf
  spec:
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
    storageClassName: csi-rbd-sc
    volumeMode: Filesystem
    volumeName: pvc-efe688d6-a420-4041-900e-c5e19fd73ebf
  status:
    accessModes:
    - ReadWriteOnce
    capacity:
      storage: 1Gi
    phase: Bound
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

mounted Filesystem size in pod using this PVC

[$]kubectl exec -it csi-rbd-demo-pod sh
# df -h /var/lib/www/html
Filesystem      Size  Used Avail Use% Mounted on
/dev/rbd0       976M  2.6M  958M   1% /var/lib/www/html

Now expand the PVC by editing the PVC (pvc.spec.resource.requests.storage)

[$]kubectl edit pvc rbd-pvc

Check PVC status after editing the pvc storage

apiVersion: v1
items:
- apiVersion: v1
  kind: PersistentVolumeClaim
  metadata:
    annotations:
      pv.kubernetes.io/bind-completed: "yes"
      pv.kubernetes.io/bound-by-controller: "yes"
      volume.beta.kubernetes.io/storage-provisioner: rbd.csi.ceph.com
    creationTimestamp: "2019-12-19T05:44:45Z"
    finalizers:
    - kubernetes.io/pvc-protection
    name: rbd-pvc
    namespace: default
    resourceVersion: "4773"
    selfLink: /api/v1/namespaces/default/persistentvolumeclaims/rbd-pvc
    uid: efe688d6-a420-4041-900e-c5e19fd73ebf
  spec:
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 10Gi
    storageClassName: csi-rbd-sc
    volumeMode: Filesystem
    volumeName: pvc-efe688d6-a420-4041-900e-c5e19fd73ebf
  status:
    accessModes:
    - ReadWriteOnce
    capacity:
      storage: 1Gi
    conditions:
    - lastProbeTime: null
      lastTransitionTime: "2019-12-19T05:49:39Z"
      message: Waiting for user to (re-)start a pod to finish file system resize of
        volume on node.
      status: "True"
      type: FileSystemResizePending
    phase: Bound
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

Now you can see the PVC status as FileSystemResizePending, once the kubelet calls the NodeExpandVolume to expand the PVC on node, the status conditions and status will be updated

[$]kubectl get pvc
NAME      STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS      AGE
rbd-pvc   Bound    pvc-efe688d6-a420-4041-900e-c5e19fd73ebf   10Gi       RWO            csi-rbd-sc   7m6s

Now let us check the directory size inside the pod where PVC is mounted

[$]kubectl exec -it csi-rbd-demo-pod sh
# df -h /var/lib/www/html
Filesystem      Size  Used Avail Use% Mounted on
/dev/rbd0       9.9G  4.5M  9.8G   1% /var/lib/www/html

now you can see the size of /var/lib/www/html is updated from 976M to 9.9G

Expand RBD Block PVC

[$]kubectl get pvc raw-block-pvc -o yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  annotations:
    pv.kubernetes.io/bind-completed: "yes"
    pv.kubernetes.io/bound-by-controller: "yes"
    volume.beta.kubernetes.io/storage-provisioner: rbd.csi.ceph.com
  creationTimestamp: "2019-12-19T05:56:02Z"
  finalizers:
  - kubernetes.io/pvc-protection
  name: raw-block-pvc
  namespace: default
  resourceVersion: "6370"
  selfLink: /api/v1/namespaces/default/persistentvolumeclaims/raw-block-pvc
  uid: 54885275-7ca9-4b89-8e7e-c99f375d1174
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: csi-rbd-sc
  volumeMode: Block
  volumeName: pvc-54885275-7ca9-4b89-8e7e-c99f375d1174
status:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 1Gi
  phase: Bound

Device size in pod using this PVC

[$]kubectl exec -it pod-with-raw-block-volume sh
sh-4.4# blockdev --getsize64 /dev/xvda
1073741824

rbd Block PVC is mounted at /dev/xvda of the pod, and the size is 1073741824 bytes which is equal to 1Gib

Now expand the PVC

To expand PVC, change (pvc.spec.resource.requests.storage) to the new size which should be greater than the current size.

[$]kubectl edit pvc raw-block-pvc

Check PVC status after editing the pvc storage

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  annotations:
    pv.kubernetes.io/bind-completed: "yes"
    pv.kubernetes.io/bound-by-controller: "yes"
    volume.beta.kubernetes.io/storage-provisioner: rbd.csi.ceph.com
  creationTimestamp: "2019-12-19T05:56:02Z"
  finalizers:
  - kubernetes.io/pvc-protection
  name: raw-block-pvc
  namespace: default
  resourceVersion: "7923"
  selfLink: /api/v1/namespaces/default/persistentvolumeclaims/raw-block-pvc
  uid: 54885275-7ca9-4b89-8e7e-c99f375d1174
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  storageClassName: csi-rbd-sc
  volumeMode: Block
  volumeName: pvc-54885275-7ca9-4b89-8e7e-c99f375d1174
status:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 1Gi
  conditions:
  - lastProbeTime: null
    lastTransitionTime: "2019-12-19T06:02:15Z"
    message: Waiting for user to (re-)start a pod to finish file system resize of
      volume on node.
    status: "True"
    type: FileSystemResizePending
  phase: Bound

Now you can see the PVC stats as FileSystemResizePending, once the kubelet calls the NodeExpandVolume to expand the PVC on node, the status conditions will be updated and status.capacity.storage will be updated.

[$]kubectl get pvc
NAME      STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS      AGE
raw-block-pvc   Bound    pvc-efe688d6-a420-4041-900e-c5e19fd73ebf   10Gi       RWO            csi-rbd-sc   7m6s

Device size in pod using this PVC

[$]kubectl exec -it pod-with-raw-block-volume sh
sh-4.4# blockdev --getsize64 /dev/xvda
10737418240

rbd Block PVC is mounted at /dev/xvda of the pod, and the size is 10737418240 bytes which is equal to 10Gib

Expand CephFS PVC

Expand CephFS Filesystem PVC

pvc.yaml

apiVersion: v1
items:
- apiVersion: v1
  kind: PersistentVolumeClaim
  metadata:
    annotations:
      pv.kubernetes.io/bind-completed: "yes"
      pv.kubernetes.io/bound-by-controller: "yes"
      volume.beta.kubernetes.io/storage-provisioner: cephfs.csi.ceph.com
    creationTimestamp: "2020-01-17T07:55:11Z"
    finalizers:
    - kubernetes.io/pvc-protection
    name: csi-cephfs-pvc
    namespace: default
    resourceVersion: "5955"
    selfLink: /api/v1/namespaces/default/persistentvolumeclaims/csi-cephfs-pvc
    uid: b84d07c9-ea67-40b4-96b9-4a79669b1ccc
  spec:
    accessModes:
    - ReadWriteMany
    resources:
      requests:
        storage: 5Gi
    storageClassName: csi-cephfs-sc
    volumeMode: Filesystem
    volumeName: pvc-b84d07c9-ea67-40b4-96b9-4a79669b1ccc
  status:
    accessModes:
    - ReadWriteMany
    capacity:
      storage: 5Gi
    phase: Bound
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

mounted Filesystem size in pod using this PVC

[$]kubectl exec -it csi-cephfs-demo-pod sh
# df -h /var/lib/www
Filesystem                                                                     Size  Used Avail Use% Mounted on
10.108.149.216:6789:/volumes/csi/csi-vol-b0a1bc79-38fe-11ea-adb6-1a2797ee96de  5.0G     0  5.0G   0% /var/lib/www

Now expand the PVC by editing the PVC (pvc.spec.resource.requests.storage)

[$]kubectl edit pvc csi-cephfs-pvc

Check PVC status after editing the PVC storage

apiVersion: v1
items:
- apiVersion: v1
  kind: PersistentVolumeClaim
  metadata:
    annotations:
      pv.kubernetes.io/bind-completed: "yes"
      pv.kubernetes.io/bound-by-controller: "yes"
      volume.beta.kubernetes.io/storage-provisioner: cephfs.csi.ceph.com
    creationTimestamp: "2020-01-17T07:55:11Z"
    finalizers:
    - kubernetes.io/pvc-protection
    name: csi-cephfs-pvc
    namespace: default
    resourceVersion: "6902"
    selfLink: /api/v1/namespaces/default/persistentvolumeclaims/csi-cephfs-pvc
    uid: b84d07c9-ea67-40b4-96b9-4a79669b1ccc
  spec:
    accessModes:
    - ReadWriteMany
    resources:
      requests:
        storage: 10Gi
    storageClassName: csi-cephfs-sc
    volumeMode: Filesystem
    volumeName: pvc-b84d07c9-ea67-40b4-96b9-4a79669b1ccc
  status:
    accessModes:
    - ReadWriteMany
    capacity:
      storage: 10Gi
    phase: Bound
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

Now you can see the PVC status capacity storage is updated with request size

[$]kubectl get pvc
NAME             STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS    AGE
csi-cephfs-pvc   Bound    pvc-b84d07c9-ea67-40b4-96b9-4a79669b1ccc   10Gi       RWX            csi-cephfs-sc   6m26s

Now let us check the directory size inside the pod where PVC is mounted

[$]kubectl exec -it csi-cephfs-demo-pod sh
#  df -h /var/lib/www
Filesystem                                                                     Size  Used Avail Use% Mounted on
10.108.149.216:6789:/volumes/csi/csi-vol-b0a1bc79-38fe-11ea-adb6-1a2797ee96de   10G     0   10G   0% /var/lib/www

now you can see the size of /var/lib/www is updated from 5G to 10G

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