Kubernetes Storage Guide – SC, PV, PVC

Complete reference for CKA. Covers binding rules, selectors, node affinity, and mounting.

1. The Three Objects

StorageClass  →  defines HOW storage is provisioned
PersistentVolume (PV)  →  actual storage resource
PersistentVolumeClaim (PVC)  →  request for storage (used by Pods)

Flow:

Pod → PVC → PV → Actual Storage (disk/NFS/cloud)
         ↑
    StorageClass (optional, defines provisioning)

2. How PVC Binds to PV (Decision Tree)

PVC Created
    │
    ▼
┌─────────────────────────────┐
│ Does PVC have `volumeName`? │
└─────────────────────────────┘
    │YES                  │NO
    ▼                     ▼
Bind to that       ┌─────────────────────────────┐
specific PV        │ Does PVC have `selector`?   │
                   └─────────────────────────────┘
                       │YES              │NO
                       ▼                 ▼
              Match PV by label    ┌─────────────────────────────┐
              + storageClass       │ Match by storageClassName   │
              + capacity           │ + capacity + accessModes    │
              + accessModes        └─────────────────────────────┘

3. Binding Rules – All Must Match

Rule	PVC Field	PV Field	Notes
StorageClass	`spec.storageClassName`	`spec.storageClassName`	Must be identical (or both empty `""`)
Capacity	`spec.resources.requests.storage`	`spec.capacity.storage`	PV capacity ≥ PVC request
Access Modes	`spec.accessModes`	`spec.accessModes`	PV must include PVC's mode
Selector	`spec.selector.matchLabels`	`metadata.labels`	PV labels must match (if selector used)
Volume Name	`spec.volumeName`	`metadata.name`	Direct binding (overrides all)

4. storageClassName Matching

PVC storageClassName	PV storageClassName	Result
`manual`	`manual`	✅ Can bind
`manual`	`other`	❌ No bind
`""` (empty string)	`""` (empty string)	✅ Can bind
(not specified)	anything	Uses default SC
`manual`	`""`	❌ No bind

Important: Empty string "" is NOT the same as omitting the field!

5. Selector-Based Binding

When PVC has a selector, it only binds to PVs with matching labels:

PV:

yaml

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-fast
  labels:
    type: ssd
    tier: premium
spec:
  capacity:
    storage: 100Mi
  accessModes: [ReadWriteOnce]
  storageClassName: ""
  hostPath:
    path: /mnt/fast

PVC:

yaml

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-ssd
spec:
  accessModes: [ReadWriteOnce]
  storageClassName: ""
  resources:
    requests:
      storage: 50Mi
  selector:
    matchLabels:
      type: ssd

Result: PVC binds to pv-fast because labels match.

6. volumeName – Direct Binding

Force PVC to bind to a specific PV (ignores capacity/selector):

yaml

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-direct
spec:
  accessModes: [ReadWriteOnce]
  storageClassName: ""
  volumeName: pv-specific  # Must match PV name exactly
  resources:
    requests:
      storage: 50Mi

Note: If PV doesn't exist or is already bound, PVC stays Pending.

7. volumeBindingMode

In StorageClass:

Mode	When PVC Binds	Use Case
`Immediate`	As soon as PVC is created	Cloud volumes, NFS
`WaitForFirstConsumer`	When Pod using PVC is scheduled	Local volumes, node-specific storage

Why WaitForFirstConsumer matters:

For local PVs, scheduler needs to know which node has the storage
Binding happens AFTER Pod scheduling decision
Required for local volume type

yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer

8. Node Affinity for Local Volumes

Local PVs must specify which node they're on:

yaml

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-local
spec:
  capacity:
    storage: 100Mi
  accessModes: [ReadWriteOnce]
  storageClassName: local-storage
  local:
    path: /mnt/data
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - worker-node-1

Pod will only run on worker-node-1 because that's where the PV is.

9. Access Modes

Mode	Abbreviation	Meaning
ReadWriteOnce	RWO	Single node, read-write
ReadOnlyMany	ROX	Multiple nodes, read-only
ReadWriteMany	RWX	Multiple nodes, read-write

hostPath and local only support RWO!

10. Reclaim Policy

What happens to PV when PVC is deleted:

Policy	PV Status After	Data	Use Case
`Retain`	`Released`	Preserved	Production data
`Delete`	PV deleted	Deleted	Temporary storage
`Recycle`	`Available`	Wiped	Deprecated

11. Mounting PVC in Pod

Basic mount:

yaml

apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: data
      mountPath: /var/data
  volumes:
  - name: data
    persistentVolumeClaim:
      claimName: my-pvc

Multiple mounts:

yaml

spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: config
      mountPath: /etc/app/config
      readOnly: true
    - name: data
      mountPath: /var/data
  volumes:
  - name: config
    persistentVolumeClaim:
      claimName: pvc-config
  - name: data
    persistentVolumeClaim:
      claimName: pvc-data

SubPath (mount specific directory):

yaml

volumeMounts:
- name: data
  mountPath: /app/logs
  subPath: logs

12. Complete Examples

Example 1: Static Provisioning (Manual PV)

yaml

# StorageClass
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: manual
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: Immediate
---
# PV
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-manual
spec:
  capacity:
    storage: 1Gi
  accessModes: [ReadWriteOnce]
  storageClassName: manual
  hostPath:
    path: /mnt/data
---
# PVC
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-manual
spec:
  accessModes: [ReadWriteOnce]
  storageClassName: manual
  resources:
    requests:
      storage: 500Mi
---
# Pod
apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  containers:
  - name: app
    image: busybox
    command: ['sleep', '3600']
    volumeMounts:
    - name: storage
      mountPath: /data
  volumes:
  - name: storage
    persistentVolumeClaim:
      claimName: pvc-manual

Example 2: Local Volume with Node Affinity

yaml

# StorageClass
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
---
# PV
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-local
spec:
  capacity:
    storage: 500Mi
  accessModes: [ReadWriteOnce]
  storageClassName: local-storage
  local:
    path: /mnt/local
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - node01
---
# PVC (stays Pending until Pod is created)
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-local
spec:
  accessModes: [ReadWriteOnce]
  storageClassName: local-storage
  resources:
    requests:
      storage: 200Mi

Example 3: Selector-Based Binding

yaml

# PV with labels
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-premium
  labels:
    tier: premium
    type: ssd
spec:
  capacity:
    storage: 100Mi
  accessModes: [ReadWriteOnce]
  storageClassName: ""
  hostPath:
    path: /mnt/premium
---
# PVC with selector
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-premium
spec:
  accessModes: [ReadWriteOnce]
  storageClassName: ""
  resources:
    requests:
      storage: 50Mi
  selector:
    matchLabels:
      tier: premium

13. Troubleshooting

PVC Stuck in Pending

bash

kubectl describe pvc <name>  # Check events
kubectl get pv               # Check available PVs
kubectl get sc               # Check StorageClasses

Common causes:

Symptom	Cause	Fix
"no persistent volumes available"	No matching PV	Create PV or check storageClassName
"storageclass not found"	SC doesn't exist	Create SC or fix PVC
"does not match"	Capacity/accessMode mismatch	Create PV with correct specs

Pod FailedMount

bash

kubectl describe pod <name>  # Check events

Common causes:

PVC not bound yet
hostPath directory doesn't exist on node
Permission issues on host directory
Node affinity mismatch (local volumes)

14. Quick Commands

bash

# List all storage objects
kubectl get sc,pv,pvc

# Check PVC binding
kubectl get pvc -o wide

# Check PV with node info
kubectl get pv -o wide

# See which PVC a PV is bound to
kubectl describe pv <name> | grep -A2 "Claim"

# Check events
kubectl describe pvc <name>

# Create directory on node for hostPath
kubectl debug node/<node> -it --image=busybox -- mkdir -p /mnt/data

15. CKA Exam Tips

Always check storageClassName matches between PVC and PV
Use kubectl get pvc -o wide to see bound PV quickly
For local volumes, always add volumeBindingMode: WaitForFirstConsumer
Empty string "" is different from not specifying storageClassName
hostPath requires directory to exist on the node
Check events with kubectl describe when things don't bind

Kubernetes Storage Guide – SC, PV, PVC ​

1. The Three Objects ​

2. How PVC Binds to PV (Decision Tree) ​

3. Binding Rules – All Must Match ​

4. storageClassName Matching ​

5. Selector-Based Binding ​

6. volumeName – Direct Binding ​

7. volumeBindingMode ​

8. Node Affinity for Local Volumes ​

9. Access Modes ​

10. Reclaim Policy ​

11. Mounting PVC in Pod ​

12. Complete Examples ​

Example 1: Static Provisioning (Manual PV) ​

Example 2: Local Volume with Node Affinity ​

Example 3: Selector-Based Binding ​

13. Troubleshooting ​

PVC Stuck in Pending ​

Pod FailedMount ​

14. Quick Commands ​

15. CKA Exam Tips ​

Kubernetes Storage Guide – SC, PV, PVC

1. The Three Objects

2. How PVC Binds to PV (Decision Tree)

3. Binding Rules – All Must Match

4. storageClassName Matching

5. Selector-Based Binding

6. volumeName – Direct Binding

7. volumeBindingMode

8. Node Affinity for Local Volumes

9. Access Modes

10. Reclaim Policy

11. Mounting PVC in Pod

12. Complete Examples

Example 1: Static Provisioning (Manual PV)

Example 2: Local Volume with Node Affinity

Example 3: Selector-Based Binding

13. Troubleshooting

PVC Stuck in Pending

Pod FailedMount

14. Quick Commands

15. CKA Exam Tips