Storage

1. Overview

What it is: Persisting bytes — block (EBS/PD), file (EFS/NFS), object (S3).

When to use: Databases (block), shared media (file), artifacts/backups (object).

When NOT to: Put databases on object storage directly unless product designed for it; use emptyDir for durable data.

2. Concepts

• Durability vs availability
• IOPS / throughput / latency
• CSI drivers in Kubernetes
• PV / PVC / StorageClass
• Access modes — RWO, ROX, RWX
• Snapshots / clones
• Filesystem choice — ext4/xfs
• Object versioning & lifecycle

3. Architecture

graph TB
  Pod --> PVC
  PVC --> PV
  PV --> CSI[CSI Driver]
  CSI --> CloudVol[EBS / Disk / NAS]
  App --> S3[Object Storage]

4. Production Best Practices

• Match volume type to workload (gp3/io2)
• Snapshots scheduled + restore tested
• Encryption by default
• Expandable StorageClasses; monitor free space/inodes
• Object lifecycle to IA/Glacier
• Backup out of account for ransomware

5. Common Mistakes

Mistake	Fix
RWX needed but RWO disk	Use NFS/EFS or redesign
No space alerts	Alert at 70/85%
Snapshots never restored	Game day
HostPath in prod	Prefer CSI

6. Debugging Guide

kubectl get pvc,pv,sc
kubectl describe pvc data
# Node
df -h; lsblk; dmesg | grep -i error

Attach failures: IAM, zone mismatch (RWO volume wrong AZ), capacity.

7. Security

• Encrypt; KMS CMKs for sensitive
• Block public S3; VPC endpoints
• Least privilege IAM for CSI roles

8. Performance

• Benchmark realistic IO; watch queue depth
• Separate WAL/data disks when advised
• Avoid noisy neighbor on shared NAS for DBs

9. Real Production Example

EBS gp3 for Postgres via CSI; daily snapshots to DR account; S3 versioned for backups; EFS for shared CMS uploads only.

10. Interview Questions

Beginner: Block vs object?

Intermediate: PVC pending causes?

Senior: Design multi-AZ storage for stateful K8s.

11. Checklist

• Encryption + snapshots
• StorageClass defaults sane
• Capacity alerts
• Backup restore tested
• AZ affinity understood

12. Cheat Sheet

Type	Example	Use
Block	EBS	DB
File	EFS	Shared files
Object	S3	Artifacts

Related Skills

• kubernetes
• databases
• disaster-recovery
• performance

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Author & maintainer: Shanmukha Kumar Karra
Created and maintained as part of AgentOps Kit.