PersistentVolume (PV) definition in Kubernetes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a PersistentVolume (PV) in Kubernetes?

A PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned by an administrator or dynamically. It is a resource in the cluster just like a node and is used to store data persistently beyond the lifecycle of a pod.

intermediate

Which key fields are required in a PersistentVolume YAML definition?

The key fields include: apiVersion, kind (PersistentVolume), metadata (name), spec (capacity, accessModes, persistentVolumeReclaimPolicy, storageClassName, and the actual storage details like hostPath, nfs, etc.).

beginner

What does the 'accessModes' field specify in a PersistentVolume?

The 'accessModes' field defines how the volume can be mounted by pods. Common modes are ReadWriteOnce (mounted by a single node), ReadOnlyMany (mounted read-only by many nodes), and ReadWriteMany (mounted read-write by many nodes).

intermediate

What is the purpose of 'persistentVolumeReclaimPolicy' in a PV?

It tells Kubernetes what to do with the volume after the claim is released. Common policies are Retain (keep data), Recycle (basic scrub), and Delete (remove volume).

beginner

Show a simple example of a PersistentVolume definition using hostPath.

apiVersion: v1 kind: PersistentVolume metadata: name: example-pv spec: capacity: storage: 1Gi accessModes: - ReadWriteOnce persistentVolumeReclaimPolicy: Retain hostPath: path: /mnt/data

What does a PersistentVolume in Kubernetes represent?

A A storage resource in the cluster

B A running container

C A network policy

D A pod specification

A PersistentVolume is a storage resource in the Kubernetes cluster used to persist data.

Which field in a PV definition specifies how the volume can be accessed by pods?

A capacity

B storageClassName

C metadata

D accessModes

The 'accessModes' field defines how pods can mount the volume.

What does the 'persistentVolumeReclaimPolicy' control?

A The size of the volume

B The access mode of the volume

C What happens to the volume after release

D The namespace of the volume

It controls what happens to the volume after the claim is released.

Which of these is NOT a valid access mode for a PersistentVolume?

A WriteOnlyOnce

B ReadOnlyMany

C ReadWriteMany

D ReadWriteOnce

'WriteOnlyOnce' is not a valid access mode in Kubernetes.

In a hostPath PersistentVolume, what does the 'path' specify?

A The network address

B The directory on the node's filesystem

C The pod name

D The storage class

The 'path' specifies the directory on the node's filesystem to use for storage.

Describe the main components and fields of a PersistentVolume definition in Kubernetes.

Think about the YAML structure and what each part means.

Explain the difference between the access modes ReadWriteOnce, ReadOnlyMany, and ReadWriteMany in PersistentVolumes.

Consider how many nodes can use the volume and in what mode.

Practice

1. What is the main purpose of a PersistentVolume (PV) in Kubernetes?

easy

A. To manage container images

B. To define network policies for pods

C. To schedule pods on specific nodes

D. To provide storage that can persist beyond the lifecycle of a pod

Solution

1. Step 1: Understand the role of PersistentVolume

   A PersistentVolume provides storage resources independent of pod lifecycle.

2. Step 2: Compare with other options

   Network policies, pod scheduling, and image management are unrelated to PV.

3. Final Answer:

   To provide storage that can persist beyond the lifecycle of a pod -> Option D

4. Quick Check:

   PV = persistent storage [OK]

Hint: PV stores data beyond pod life, not network or scheduling [OK]

Common Mistakes:

• Confusing PV with pod scheduling
• Thinking PV manages network policies
• Assuming PV handles container images

2. Which of the following is the correct minimal YAML snippet to define a PersistentVolume with 5Gi storage and ReadWriteOnce access mode?

easy

A. apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-example\nspec:\n capacity:\n storage: 5GB\n accessModes:\n - ReadOnlyMany\n hostPath:\n path: /mnt/data

B. apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-example\nspec:\n capacity:\n storage: 5Gi\n accessModes:\n - ReadWriteOnce\n hostPath:\n path: /mnt/data

C. apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-example\nspec:\n size: 5Gi\n accessModes:\n - ReadWriteMany\n hostPath:\n path: /mnt/data

D. apiVersion: v1\nkind: PersistentVolumeClaim\nmetadata:\n name: pvc-example\nspec:\n storage: 5Gi\n accessModes:\n - ReadWriteOnce

Solution

1. Step 1: Check correct kind and apiVersion

   PersistentVolume uses kind: PersistentVolume and apiVersion: v1.

2. Step 2: Validate capacity and accessModes syntax

   Capacity must be under spec.capacity.storage with unit Gi, and accessModes is a list with ReadWriteOnce.

3. Final Answer:

   YAML with capacity 5Gi, accessModes ReadWriteOnce, kind PersistentVolume -> Option B

4. Quick Check:

   Correct YAML keys and values = apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-example\nspec:\n capacity:\n storage: 5Gi\n accessModes:\n - ReadWriteOnce\n hostPath:\n path: /mnt/data [OK]

Hint: PV uses spec.capacity.storage with units like Gi, not size or GB [OK]

Common Mistakes:

• Using PersistentVolumeClaim instead of PersistentVolume
• Wrong key 'size' instead of 'capacity.storage'
• Incorrect storage unit like GB instead of Gi
• Wrong access mode or misspelled keys

3. Given this PersistentVolume YAML snippet, what is the reclaim policy of the PV?

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-sample
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  hostPath:
    path: /mnt/data

medium

A. Delete the volume after release

B. Recycle the volume automatically

C. Retain the volume after release

D. No reclaim policy set

Solution

1. Step 1: Locate the reclaim policy field

   The field persistentVolumeReclaimPolicy is set to Retain in the spec.

2. Step 2: Understand reclaim policy meaning

   Retain means the volume is kept after the claim is released, not deleted or recycled.

3. Final Answer:

   Retain the volume after release -> Option C

4. Quick Check:

   persistentVolumeReclaimPolicy = Retain [OK]

Hint: Look for persistentVolumeReclaimPolicy field value [OK]

Common Mistakes:

• Confusing Retain with Delete or Recycle
• Ignoring the reclaim policy field
• Assuming default policy without checking

4. You defined this PersistentVolume YAML but get an error when applying it:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-error
spec:
  capacity:
    storage: 20Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Delete
  hostPath:
    path: /mnt/data
  storageClassName: fast

What is the likely cause of the error?

medium

A. hostPath volumes cannot have storageClassName set

B. accessModes value ReadWriteOnce is invalid

C. Missing volumeMode field

D. persistentVolumeReclaimPolicy Delete is not allowed

Solution

1. Step 1: Check hostPath volume restrictions

   hostPath volumes do not support storageClassName because they are local paths.

2. Step 2: Validate other fields

   accessModes and reclaim policy values are valid; volumeMode is optional.

3. Final Answer:

   hostPath volumes cannot have storageClassName set -> Option A

4. Quick Check:

   hostPath + storageClassName = error [OK]

Hint: hostPath volumes must not set storageClassName [OK]

Common Mistakes:

• Assuming volumeMode is mandatory
• Thinking accessModes ReadWriteOnce is invalid
• Believing Delete reclaim policy is disallowed

5. You want to create a PersistentVolume that allows multiple pods to read and write simultaneously and automatically deletes the volume when released. Which YAML snippet correctly defines these requirements?

hard

A. apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-multi\nspec:\n capacity:\n storage: 15Gi\n accessModes:\n - ReadWriteMany\n persistentVolumeReclaimPolicy: Delete\n nfs:\n path: /exports/data\n server: 10.0.0.1

B. apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-single\nspec:\n capacity:\n storage: 15Gi\n accessModes:\n - ReadWriteOnce\n persistentVolumeReclaimPolicy: Retain\n hostPath:\n path: /mnt/data

C. apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-multi\nspec:\n capacity:\n storage: 15Gi\n accessModes:\n - ReadOnlyMany\n persistentVolumeReclaimPolicy: Delete\n nfs:\n path: /exports/data\n server: 10.0.0.1

D. apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-multi\nspec:\n capacity:\n storage: 15Gi\n accessModes:\n - ReadWriteMany\n persistentVolumeReclaimPolicy: Retain\n nfs:\n path: /exports/data\n server: 10.0.0.1

Solution

1. Step 1: Identify access mode for multiple pods read/write

   ReadWriteMany allows multiple pods to read and write simultaneously.

2. Step 2: Check reclaim policy for automatic deletion

   persistentVolumeReclaimPolicy: Delete deletes the volume after release.

3. Step 3: Confirm storage type supports ReadWriteMany

   NFS supports ReadWriteMany; hostPath does not.

4. Final Answer:

   YAML with ReadWriteMany, Delete reclaim policy, and NFS volume -> Option A

5. Quick Check:

   ReadWriteMany + Delete + NFS = apiVersion: v1\nkind: PersistentVolume\nmetadata:\n name: pv-multi\nspec:\n capacity:\n storage: 15Gi\n accessModes:\n - ReadWriteMany\n persistentVolumeReclaimPolicy: Delete\n nfs:\n path: /exports/data\n server: 10.0.0.1 [OK]

Hint: Use ReadWriteMany + Delete + NFS for multi-pod writable PV [OK]

Common Mistakes:

• Using hostPath for multi-pod access
• Choosing ReadWriteOnce instead of ReadWriteMany
• Setting reclaim policy to Retain instead of Delete