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💾 Persistent Volume (PV) in Kubernetes

Definition:

A Persistent Volume (PV) is a storage resource in Kubernetes that exists independently of pods and provides durable storage for containers.

  • Pods are ephemeral → their filesystem disappears when deleted.
  • PV allows data to persist beyond pod lifecycle.

1️⃣ Key Concepts

a) Persistent Volume (PV)

  • Cluster-level resource representing actual storage (e.g., NFS, EBS, GCE Persistent Disk).
  • Created by admin or dynamically via StorageClass.
  • Has capacity, access modes, and reclaim policy.

b) Persistent Volume Claim (PVC)

  • Request for storage by a pod.
  • Specifies size, access mode.
  • Kubernetes binds PVC to a suitable PV.

c) StorageClass

  • Defines type of storage (fast SSD, slow HDD, cloud-managed).
  • Supports dynamic provisioning → PV is created automatically when PVC is requested.

2️⃣ How It Works (Flow)

Pod --> PVC --> PV --> Storage Backend
  1. Pod requests storage via PVC.
  2. Kubernetes finds matching PV or creates one dynamically.
  3. PV is mounted to pod.
  4. Data persists even if pod is deleted/recreated.

3️⃣ Access Modes

Mode Meaning
ReadWriteOnce Mounted as read/write by a single node
ReadOnlyMany Mounted read-only by multiple nodes
ReadWriteMany Mounted read/write by multiple nodes

4️⃣ Reclaim Policies

Policy Meaning
Retain PV and data are kept after PVC deletion
Delete PV and storage deleted when PVC deleted
Recycle PV is cleaned and reused

5️⃣ Analogy

Think of PV like a hard drive and PVC like a request to rent that hard drive:

  • Pod = user who needs storage
  • PV = actual storage device
  • PVC = lease agreement specifying size and access
  • Data stays safe even if the user (pod) leaves

💡 Key takeaway:

  • PV = durable, cluster-level storage
  • PVC = pod’s request for storage
  • Decouples storage lifecycle from pod lifecycle

💡 Persistent Volume Claim (PVC) in Kubernetes

Definition:

A Persistent Volume Claim (PVC) is a request for storage by a pod. It specifies size, access mode, and storage class, and Kubernetes binds it to a suitable Persistent Volume (PV).

  • PVC is how pods consume storage in Kubernetes.
  • Decouples storage request from physical storage details.

1️⃣ How PVC Works

  1. Pod needs storage → defines a PVC in its spec.
  2. Kubernetes looks for a matching PV (capacity, access mode, storage class).
  3. If a match is found, PV is bound to PVC.
  4. Pod mounts PVC → can read/write data.

Flow (Text Diagram):

Pod --> PVC --> PV --> Storage Backend
  • Pod asks for storage → PVC → Kubernetes finds or provisions PV → Pod uses PV.

2️⃣ Key Fields in PVC

Field Description
resources.requests.storage Amount of storage requested (e.g., 10Gi)
accessModes Read/write permissions (ReadWriteOnce, ReadOnlyMany, ReadWriteMany)
storageClassName Type of storage / provisioner (e.g., fast SSD, standard HDD)

3️⃣ Dynamic vs Static Provisioning

  • Static Provisioning: PV is pre-created by admin, PVC binds to it.
  • Dynamic Provisioning: PVC triggers automatic creation of PV via StorageClass.

4️⃣ Benefits

  • Decouples storage from pod lifecycle → data persists beyond pod.
  • Standardizes storage requests → pods don’t need to know physical storage details.
  • Supports dynamic provisioning → automatically allocate new PVs.

5️⃣ Analogy

Think of PVC like a storage rental request:

  • Pod = tenant needing storage
  • PVC = rental request specifying size & type
  • PV = actual storage drive / warehouse
  • Kubernetes binds the request → tenant gets storage
  • Data persists even if tenant moves out (pod deleted)

💡 Key takeaway:

  • PVC = pod’s request for storage
  • PV = physical storage
  • PVC abstracts how storage is allocated, making it easy and reusable