At work, I manage extensive datasets across Amazon S3 and traditional file systems like EFS and FSx. The release of Amazon S3 Files caught my attention because it provides a POSIX interface directly over an S3 bucket, allowing you to mount it like a standard network drive and use normal file operations. The capability is excellent, but deciding between S3 Files and EFS is not entirely straightforward, particularly regarding pricing. I spent some time researching the architectural and cost trade-offs to clarify when to use each.
Architecture scenarios
S3 Files has a specific caching architecture. Small files and active metadata sit in a high-performance cache. Large files of 1 MiB and above are streamed directly from the underlying S3 bucket when read. S3 Files does not support hard links, file locking, or file-based databases. There is also a write-back delay of around 60 seconds before changes sync to S3.
When S3 Files works well
S3 Files is an excellent fit for read-heavy workloads processing large objects. If you are running containerised applications on ECS Fargate that need to serve large GIS Mapfiles, satellite imagery, or extensive spatial datasets, S3 Files streams these payloads directly from S3. The application treats the data as local files, and you bypass the complexity of rewriting your code to use API-based object retrieval.
When EFS remains the better choice
EFS is necessary when you need strict read-after-write consistency across multiple concurrent instances. If you are configuring a busy Apache reverse proxy with a heavy map tile disk cache comprising millions of tiny images, S3 Files is unsuitable. The small files would constantly hit the high-performance cache layer, removing the cost advantage. Similarly, if your application requires file locking to prevent corruption during concurrent writes, or if you are running a file-based database, EFS provides the required POSIX guarantees.
Pricing breakdown
The primary cost difference lies in how the two services handle storage and data access.
- EFS Standard: Costs $0.30 per GB-month. You also pay for throughput if your workload requires Provisioned Throughput rather than bursting, which costs an extra $6.60 per MBps-month. Using EFS lifecycle policies can drop the effective rate to roughly $0.03 per GB-month by moving cold data to Infrequent Access or Archive tiers, but this relies on data remaining untouched for 30 to 90 days.
- S3 Files: The underlying S3 storage costs the standard rate of $0.023 per GB-month. The high-performance cache for small files and metadata costs $0.30 per GB-month, alongside small charges for cache reads and writes. Large files (1 MiB and above) incur no cache storage or data access charges because they stream directly from S3.
For a workload consisting primarily of large files, S3 Files is roughly 13 times cheaper than EFS before factoring in any EFS throughput charges. However, if your data comprises mostly small files, S3 Files ends up more expensive than EFS because all the data sits in the cache tier.
Here is a calculator to visualise the cost difference based on the file size distribution of a workload.
EFS vs S3 Files cost simulator