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How EFS works

Elastic, fully managed NFS file system shared by thousands of clients across AZs. Throughput scales automatically (Elastic) or is provisioned in MB/s. Writes cost three times what reads do, and the elastic write ceiling is far below the read ceiling.

Sometimes many servers need to share the same files at the same time, a content directory, user uploads, a shared workspace. EBS can’t do that (one disk, one instance). EFS can: it’s a managed shared filesystem that any number of instances and containers mount at once, spanning multiple AZs and growing elastically on its own.

What you will learn

What gap does a shared filesystem fill that EBS can’t?
How can many instances safely read/write the same EFS files?
Why is EFS "elastic" and multi-AZ, and what does that buy you?
When EFS vs EBS vs S3?

Many readers and writers, one filesystem

EFS is a managed NFS filesystem with POSIX semantics. Multiple EC2 instances and containers mount it simultaneously and see the same directory tree, so they share files in real time, something a single-attach EBS volume can’t provide.

Elastic and multi-AZ

EFS grows and shrinks automatically as you add or remove files, no capacity to provision. It also stores data across multiple Availability Zones, so it stays available if an AZ fails and any-AZ instances can reach it.

⚓ Shared web content, CMS uploads, container shared volumes, home directories, and lift-and-shift apps expecting a POSIX filesystem.

Cost: storage classes and lifecycle

EFS has storage classes (Standard, Infrequent Access, and the colder Archive) and lifecycle management that automatically tiers files into IA (after ~30 days untouched) and Archive (after ~90), cutting cost for cold files in an otherwise hot filesystem.

EFS vs EBS vs S3

EBS: a fast disk for one instance. EFS: a shared POSIX filesystem for many instances across AZs. S3: object storage over HTTP for unlimited blobs, not a mountable filesystem.

Flashcards

What can EFS do that EBS can’t?: Let many instances/containers mount and share the same files concurrently (NFS/POSIX), across AZs, EBS attaches to one instance.
Do you provision EFS capacity?: No, it’s elastic, growing and shrinking automatically as files are added or removed, and it spans multiple AZs.
What does EFS being multi-AZ give you?: Availability through an AZ failure, and access from instances in any AZ to the same filesystem.
How does EFS cut cost for cold files, and what’s the catch overall?: Lifecycle moves untouched files to Infrequent Access. Catch: EFS costs more per GB than EBS/S3, use it when you truly need shared files.
EBS vs EFS vs S3 in one line?: EBS = one-instance block disk; EFS = shared multi-instance filesystem; S3 = object storage over HTTP.

Sources

Open the SysPad canvas · Official EFS documentation