💾 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
- Pod requests storage via PVC.
- Kubernetes finds matching PV or creates one dynamically.
- PV is mounted to pod.
- 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
- Pod needs storage → defines a PVC in its spec.
- Kubernetes looks for a matching PV (capacity, access mode, storage class).
- If a match is found, PV is bound to PVC.
- 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