Do I need to choose a size for EFS in advance, like I do with EBS?

No — EFS grows and shrinks automatically as files are added or removed, so there is no capacity to provision up front. An EBS volume, by contrast, has a size you set and can later resize as a deliberate action.

Is EFS just a network version of EBS?

Not quite — the key difference is not just location but shape. EBS presents a raw block-level disk to one instance; EFS presents a genuine shared file system, with folders, that many instances mount and use at once. They solve different problems rather than being the same thing over a different connection.

Where does Amazon S3 fit next to EBS and EFS?

S3 is a third option for a different job again: it stores whole objects accessed over the web by key, with no disk or mount point involved, which suits files and backups rather than an instance’s own disk (EBS) or a shared mounted file system (EFS).

Cloud basics

EBS vs EFS: which AWS storage should you use?

Q: Are EBS and EFS both tested on AWS certifications?

Yes — telling block storage, shared file storage and object storage apart is core material on AWS Certified Solutions Architect – Associate, with the basics introduced on AWS Certified Cloud Practitioner.

By the SaveMyCert Editorial TeamPublished 17 Sept 2026Updated 17 Sept 2026

Amazon EBS is block storage that attaches to a single EC2 instance and behaves like that instance’s private disk, while Amazon EFS is a shared, elastic file system that many EC2 instances can mount and use at the same time — the choice comes down to whether one server needs a disk or several servers need to share files. Both are AWS storage services that pair with EC2, and both come up constantly once an application grows beyond a single machine, but they solve different problems and are not interchangeable. This guide sets out what each one is, the differences that decide between them, and when to reach for each.

What each one is, briefly

Amazon EBS provides a block-storage volume: a virtual disk that attaches to one EC2 instance at a time and behaves like that instance’s own internal hard drive, used for an operating system boot volume or the storage behind an application or database running on that instance. Our what-is-amazon-ebs explainer covers it in depth.

Amazon EFS provides a shared file system: it can be mounted by many EC2 instances at once, all reading and writing the same files and folders, and it grows and shrinks automatically as data is added or removed rather than needing a size chosen up front. Our what-is-amazon-efs explainer covers it separately.

Amazon S3 is worth a one-line mention here too, since it is the third storage service EC2 workloads often reach for: it stores whole objects accessed over the web by key, rather than acting as a disk or a mounted file system, which makes it a fit for files and backups rather than for either of the two use cases below.

The key differences

The practical distinctions that decide between them:

Attachment — an EBS volume attaches to a single EC2 instance at a time; an EFS file system can be mounted by many EC2 instances simultaneously.
Storage model — EBS presents a raw block-level volume, the way a physical disk does; EFS presents a real file system with folders, mounted and used with ordinary file operations.
Sharing — EBS is not designed for several instances to read and write the same volume concurrently; EFS is built precisely for that concurrent, shared access.
Capacity — an EBS volume has a size you provision and can resize as a deliberate action; EFS grows and shrinks automatically with no size to choose up front.
Typical role — EBS usually plays the part of an instance’s own disk (OS volume, or the storage behind a database on that instance); EFS usually plays the part of shared storage a fleet of instances depends on together.

When to choose EBS

Reach for EBS when a single EC2 instance needs its own disk — the operating system volume it boots from, or the storage volume behind a database or application that expects a conventional block-level disk underneath it. If nothing else on the network needs to touch that data directly, EBS is the natural fit.

When to choose EFS

Reach for EFS when more than one EC2 instance needs to read and write the same files at the same time — shared web content behind a load balancer, a lift-and-shift application that already expects a network file system, or any fleet of instances that must stay consistent on a shared file tree. If the requirement is “several servers, one set of files,” EBS cannot do that job; EFS can.

The honest answer: not really competitors

EBS and EFS are rarely a genuine either/or decision, because they usually answer different questions within the same architecture rather than competing for the same job. A common pattern is an EC2 instance using an EBS volume for its own operating system and local data, while a separate fleet of instances mounts an EFS file system for the content or datasets they need to share. Choosing between them is less “which is better” and more “does this data belong to one instance or several.”

Where this appears in certification study

Distinguishing block storage from shared file storage — and choosing correctly between EBS and EFS for a given scenario — is core material on AWS Certified Solutions Architect – Associate, with the basic distinction introduced on AWS Certified Cloud Practitioner. The exam-depth detail on configuring either service belongs in our /revision study material.

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Questions, answered

Generally no — an EBS volume is designed to attach to a single EC2 instance at a time and behaves like that instance’s private disk. Sharing the same storage across many instances concurrently is what EFS is built for instead.