1. What is Amazon EFS?

Amazon Elastic File System is a fully managed, serverless, elastic NFS (Network File System) that can be shared across multiple EC2 instances, Lambda functions, and ECS/EKS containers simultaneously.

EFS vs EBS vs S3 EBS = block storage, attached to ONE EC2 instance (one AZ). S3 = object storage, accessed via HTTP API. EFS = file storage (NFS), shared across MANY instances simultaneously, across multiple AZs. Think: EFS is a shared network drive.

2. Key Characteristics

  1. NFS v4.1 protocol — Linux only (not Windows)
  2. Multi-AZ: accessible from any AZ in the Region simultaneously
  3. Automatically grows and shrinks (no capacity provisioning needed)
  4. Can scale to petabytes. Thousands of concurrent connections.
  5. Pay-per-use: charged per GB stored (no upfront provisioning)
  6. Encryption at rest (KMS) and in transit (TLS)
  7. Accessible from on-premises via AWS Direct Connect or VPN
  8. Compatible with: EC2, ECS, EKS, Fargate, Lambda

3. EFS Performance Modes

4. EFS Throughput Modes

5. EFS Storage Classes

  1. EFS Lifecycle Policy automatically moves files between Standard and IA tiers based on last access time (7, 14, 30, 60, 90 days)
  2. EFS Intelligent-Tiering moves files automatically between all tiers

6. EFS vs EBS Comparison

7. EFS vs EBS Comparison

Use EFS when you need a shared, scalable NFS file system accessible by multiple EC2 instances or containers simultaneously.

Key exam triggers:

  1. "shared file system"
  2. "NFS"
  3. "Multiple instances access the same files."
  4. "auto-scaling storage"
  5. "Linux file system"
  6. "container shared storage."

Common scenarios:

  1. Web servers share content across multiple EC2 instances.
  2. Container storage for ECS/EKS/Fargate.
  3. Home directories for users across instances.
  4. CMS/media processing where multiple instances read/write the same files.
  5. Big data and analytics need shared access.
  6. Lift-and-shift on-premises NFS workloads.


Exam Tip EFS questions: "Shared file storage across multiple EC2 instances" = EFS. "Linux only" = EFS (not Windows). "Auto-scaling file system" = EFS. "Lambda needs persistent shared storage" = EFS. "Windows shared storage" = FSx for Windows (not EFS). EFS is ~3x more expensive than EBS per GB, but eliminates capacity planning.