What is Amazon EFS? A plain-English explainer

What file storage actually is

File storage organises data into files arranged in a hierarchy of folders — the model most people already know from a desktop computer or a shared office drive — and it can be exposed over the network so more than one computer can access the same folder structure at once. That is a genuinely different model from block storage, which presents a raw volume that behaves like a single computer’s private disk, and from object storage, which stores whole files as objects addressed by a key over HTTP rather than through folders. Our object-vs-block-vs-file-storage explainer lays out all three in one place.

EFS versus EBS: shared versus single-instance

The clearest way to understand EFS is against Amazon EBS, since both are commonly used alongside EC2. An EBS volume attaches to one EC2 instance at a time and behaves like that instance’s private disk — if a second instance needs the same data, it needs its own copy or its own volume. EFS is the opposite shape: it is a single shared file system that many EC2 instances can mount concurrently, all reading and writing the same files. Our what-is-amazon-ebs explainer covers the single-instance side in full. The choice between the two comes down to one question: does one server need a disk, or do several servers need to share a file system.

EFS versus S3: file semantics versus objects

EFS is also easy to confuse with Amazon S3, since both can hold large amounts of shared data. The difference is in how that data is accessed. EFS behaves like a real file system — an EC2 instance mounts it and reads and writes files and directories using ordinary file operations, exactly as it would with a local folder. S3 stores whole objects retrieved over HTTP by key, with no true folder hierarchy underneath and no “mount” in the file-system sense. An application built around ordinary file reads and writes generally wants EFS; an application built around fetching whole files by name over the network generally wants S3.

Elasticity, in one line

EFS grows and shrinks automatically as files are added and removed, so there is no volume size to choose up front and no resizing operation to perform later — the file system simply reflects however much data is currently stored in it. This is the “elastic” in the name, and it is one of the main practical differences from EBS, where a volume has a size you set (and can later change, but as a deliberate action).

Common uses

EFS tends to appear specifically where more than one server needs the same files at the same time:

• Shared web content — multiple web or application servers behind a load balancer serving the same uploaded content or code.
• Lift-and-shift applications — existing on-premises applications that were already built around a shared network file system and expect one in the cloud.
• Content management and shared home directories — workloads where several instances need consistent, simultaneous access to the same file tree.
• Big data and analytics workloads — tools that read and write large shared datasets across a fleet of processing instances.

Where EFS appears in certification study

EFS is introduced alongside EBS and S3 on AWS Cloud Practitioner, mainly so learners can tell the three storage models apart. It is covered in more depth on AWS Certified Solutions Architect – Associate, which expects you to choose EFS correctly for shared-storage scenarios, and on AWS Certified CloudOps Engineer – Associate, which covers mounting, monitoring and operating file systems day to day. Our /revision study library covers that depth lesson by lesson.