AWS Certified Cloud Practitioner / EC2 Instance Storage

Amazon EFS Overview

📂 Amazon EFS (Elastic File System)

EBS attaches to one EC2 instance at a time. EFS solves the opposite problem: a fully managed, shared network file system that many Linux EC2 instances can mount and access simultaneously — like a shared network drive in the cloud.

🌐 How It Works

Built on NFS (Network File System) — storage accessed over the network, not attached locally.

  • Every connected instance sees the same folders, files, and directory structure

  • One instance's changes are instantly visible to all others

  • No copying, no snapshots needed just to share files

🚀 Key Features

  • 📂 Shared storage — 2, 20, or hundreds of instances can mount the same file system

  • 🌍 Multi-AZ — accessible across Availability Zones in the same Region (EBS is single-AZ)

  • 📈 Auto-scales — grows and shrinks with your files, no capacity planning

  • 💳 Pay-per-use — billed only for storage actually consumed

  • 🐧 Linux only — Windows uses Amazon FSx for Windows File Server instead

💡 Cost note: EFS runs roughly 3× the price of a gp2 EBS volume — the premium buys shared access, multi-AZ resilience, and auto-scaling.

⚖️ EBS vs EFS

Feature

📀 EBS

📂 EFS

Storage type

Block storage

Shared network file system

Multi-instance access

❌ (one at a time)

✅

Availability Zone

Single AZ

Multiple AZs

OS support

Linux & Windows

Linux only

Auto-scaling

❌

✅

Best for

Individual instance storage

Shared file storage

💡 Beginner tip: EBS = your own personal hard drive. EFS = one shared network folder everyone works from.

🗄️ Storage Classes

  • 📂 EFS Standard — default, best performance, for frequently accessed files

  • 💰 EFS Infrequent Access (EFS-IA) — for rarely touched files, up to 92% cheaper than Standard

🔄 Lifecycle Management

Automatically moves files between classes based on access patterns — no manual work, fully transparent to your application.

Example policy: move files untouched for 60 days into EFS-IA.

  • File accessed daily → stays in Standard

  • File untouched 60+ days → auto-moves to EFS-IA

  • File reopened later → auto-moves back to Standard

Your app reads files the same way regardless of which class they're in.

🎯 Exam Cheat Sheet

  • EFS = fully managed NFS, Linux-only

  • Multiple instances, multiple AZs, simultaneous access

  • Auto-scales, pay-as-you-go

  • ~3× cost of gp2 EBS

  • Standard vs IA (up to 92% cheaper), moved automatically via Lifecycle Management

  • Exam clue "shared storage, multiple instances, multiple AZs" → EFS

  • Quick rule: EBS = one instance, one volume. EFS = many instances, one shared file system.