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Amazon EFS (Elastic File System)

Amazon EFS (Elastic File System) is AWS's managed NFSv4 network filesystem service — an elastic, multi-AZ, POSIX-semantics filesystem accessible from EC2, containers, and Lambda. In the 2026-04-07 "S3 Files" launch, EFS was confirmed as the under-the-covers backing for the S3 Files high-performance storage tier, delivering ~1 ms latencies for active data (Stormacq 2026-04-07 News Blog).

(Source: sources/2026-04-07-allthingsdistributed-s3-files-and-the-changing-face-of-s3)

Role in S3 Files

  • EFS provides the file-optimised namespace attached to an S3 bucket or prefix when a customer mounts it via systems/s3-files.
  • NFS close-to-open consistency, directory operations, permission checks, inode semantics — all the standard filesystem contracts applications expect — are delivered by EFS.
  • The S3 Files sync layer propagates changes between EFS and S3 (concepts/stage-and-commit) roughly every 60 seconds.

Why EFS (not a greenfield filesystem)

  • Mature NFS semantics — the service customers already use as their managed shared filesystem on AWS.
  • Elastic + multi-AZ — matches S3's elasticity property; no pre-provisioned capacity tier the customer has to manage.
  • Existing integration surface — EC2/ECS/EKS/Lambda NFS mounting is already supported across the AWS compute stack.

Historical positioning vs. S3

Until 2026-04, EFS and S3 sat as parallel storage options forcing an early architecture choice:

"Builders hate the fact that they have to decide early on whether their data is going to live in a file system or an object store, and to be stuck with the consequences of that from then on."

The initial EFS-meets-S3 design explored through most of 2024 (nicknamed "EFS3" internally) attempted to converge them into one unified system. That effort failed — see systems/s3-files for the design story. The resolution preserves EFS and S3 as distinct storage presentations and makes S3 Files the bridge between them.

Caveats

  • This wiki page records EFS as it appears in the 2026-04-07 post: the under-the-covers backing for S3 Files. Detailed EFS architecture (burst-credit-less General Purpose and Elastic performance modes, One Zone storage classes, EFS-specific NFSv4.1 extensions) is not in scope of that post.
  • No internal architecture of EFS itself is described — how the sync layer integrates with EFS at the backend is not public.

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