🧵 Kubernetes Storage — Masterclass Thread 👇👇 From EmptyDir → PV/PVC...
Rakesh Jain@devops_tech
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Dec 18, 2025
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🧵 Kubernetes Storage — Masterclass Thread 👇👇
From EmptyDir → PV/PVC → StorageClasses → CSI → Dynamic Provisioning
#Kubernetes #Storage #DevOps
From EmptyDir → PV/PVC → StorageClasses → CSI → Dynamic Provisioning
#Kubernetes #Storage #DevOps
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1️⃣ Storage in k8s ≠ Storage on nodes
Kubernetes does not store data itself.
It only orchestrates how your Pods claim storage from underlying systems (EBS, NFS, Ceph, local disks, etc.)
This abstraction gives portability.
Kubernetes does not store data itself.
It only orchestrates how your Pods claim storage from underlying systems (EBS, NFS, Ceph, local disks, etc.)
This abstraction gives portability.
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2️⃣ Volume: The simplest unit
A volume lives as long as the Pod.
Examples:
emptyDir → temporary workspace
hostPath → use node’s filesystem
Great for build pods, CI pipelines, caches — not for real data.
A volume lives as long as the Pod.
Examples:
emptyDir → temporary workspace
hostPath → use node’s filesystem
Great for build pods, CI pipelines, caches — not for real data.
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3️⃣ Why Persistent Volumes (PV)?
Pods die → volumes die
Apps need data that outlives pods (DB, MQ, CMS, etc.)
Enter PV + PVC model:
PV → actual storage (NFS, EBS, Ceph, SAN)
PVC → user request for storage
Pods die → volumes die
Apps need data that outlives pods (DB, MQ, CMS, etc.)
Enter PV + PVC model:
PV → actual storage (NFS, EBS, Ceph, SAN)
PVC → user request for storage
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4️⃣ PV + PVC = Decoupling
Developers request storage
Ops teams manage backend storage
Example PVC:
If this matches a PV → bound
Developers request storage
Ops teams manage backend storage
Example PVC:
If this matches a PV → bound
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5️⃣ Access Modes — Most misunderstood
Most cloud disks support RWO,
Distributed FS (NFS, CephFS, EFS) support RWX.
Most cloud disks support RWO,
Distributed FS (NFS, CephFS, EFS) support RWX.
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6️⃣ StorageClasses — default brain of provisioning
Without StorageClass → you must manually create PVs
With StorageClass → volumes get auto-created
“Kubernetes, give me 20Gi storage”…
“Done.”
Example:
Without StorageClass → you must manually create PVs
With StorageClass → volumes get auto-created
“Kubernetes, give me 20Gi storage”…
“Done.”
Example:
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7️⃣ Reclaim Policies
Defines what happens to PV after PVC is deleted:
Delete → storage destroyed
Retain → manual cleanup needed
Recycle (deprecated)
Production DBs often use Retain.
Defines what happens to PV after PVC is deleted:
Delete → storage destroyed
Retain → manual cleanup needed
Recycle (deprecated)
Production DBs often use Retain.
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8️⃣ Dynamic Provisioning — The magic
PVC auto-creates storage using StorageClass.
PVC:
Kubernetes:
🪄 “Creating EBS volume…”
🪄 “Attaching to node…”
🪄 “Mounting into Pod…”
PVC auto-creates storage using StorageClass.
PVC:
Kubernetes:
🪄 “Creating EBS volume…”
🪄 “Attaching to node…”
🪄 “Mounting into Pod…”
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9️⃣ CSI — Container Storage Interface
CSI makes storage plugin based.
No more in-tree drivers.
Supports block, file, snapshots, resizing.
Common CSI drivers:
AWS EBS
Azure Disk/File
GCP PD
Ceph RBD / CephFS
Longhorn
OpenEBS
vSphere CSI
NFS CSI
CSI makes storage plugin based.
No more in-tree drivers.
Supports block, file, snapshots, resizing.
Common CSI drivers:
AWS EBS
Azure Disk/File
GCP PD
Ceph RBD / CephFS
Longhorn
OpenEBS
vSphere CSI
NFS CSI
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🔟 Volume Snapshots
Database backups got easier.
SnapshotClass + VolumeSnapshot.
Example:
Database backups got easier.
SnapshotClass + VolumeSnapshot.
Example:
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1️⃣1️⃣ Volume Expansion
Resize PVC without deleting Pod (if driver supports it).
Resize PVC without deleting Pod (if driver supports it).
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1️⃣2️⃣ Local Persistent Volumes
Fastest storage available → local SSDs
But Pod must run on same node → use nodeAffinity.
Great for Kafka, Elastic, Redis.
Fastest storage available → local SSDs
But Pod must run on same node → use nodeAffinity.
Great for Kafka, Elastic, Redis.
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1️⃣3️⃣ Real-World Examples
Example: MySQL with persistent storage
Example: MySQL with persistent storage
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Example: WordPress shared uploads using RWX
Backed by NFS or EFS:
accessModes: ["ReadWriteMany"]
Multiple replicas can write to the same folder.
Backed by NFS or EFS:
accessModes: ["ReadWriteMany"]
Multiple replicas can write to the same folder.
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1️⃣4️⃣ Common Mistakes
❌ Using hostPath in production
❌ Using RWO volumes with multiple pods
❌ Using local PVs without nodeAffinity
❌ Forgetting Retain/Delete policy
❌ Storing DB on emptyDir
❌ Using hostPath in production
❌ Using RWO volumes with multiple pods
❌ Using local PVs without nodeAffinity
❌ Forgetting Retain/Delete policy
❌ Storing DB on emptyDir
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1️⃣5️⃣ Quick Cheatsheet
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1️⃣6️⃣ TL;DR
Kubernetes storage is powerful when you follow the chain:
Volume → PersistentVolume → PersistentVolumeClaim → StorageClass → CSI → Snapshots
Master this, and you can run ANY stateful workload on Kubernetes confidently.
#Kubernetes #Storage #DevOps
Kubernetes storage is powerful when you follow the chain:
Volume → PersistentVolume → PersistentVolumeClaim → StorageClass → CSI → Snapshots
Master this, and you can run ANY stateful workload on Kubernetes confidently.
#Kubernetes #Storage #DevOps
