How to Share 25 GB Files Across EC2 Instances and Multiple AZs?
Short answer
C Mounting an Amazon EFS file system across all EC2 instances provides shared, Multi-AZ file access for the 25 GB files without copying between instances.
Question
Key Takeaways
The question tests shared, Multi-AZ POSIX file storage for large files on Linux EC2 instances; the trap is choosing S3 (object storage, not a mounted shared file system for the application) or an EBS snapshot (which cannot be mounted on many instances in multiple AZs).
When EC2 applications must store and retrieve 25 GB files that are shared across many instances and multiple Availability Zones without copying files between instances, Amazon EFS is the storage service that satisfies every requirement. This page confirms why the EFS option (C) is correct and why S3, EBS snapshots, and instance store volumes do not fit this scenario.
Common mistake: Many candidates pick Amazon S3 (A) because it is durable, shared, and Multi-AZ, but S3 is object storage accessed by API rather than a POSIX file system mounted on the instances, so the existing EC2 applications would have to be rewritten instead of simply reading and writing 25 GB files as files.
Expert Analysis
Why the Answer Is Correct
Amazon EFS is a fully managed, elastic NFS file system that can be mounted simultaneously on thousands of Linux EC2 instances, including instances spread across multiple Availability Zones in the same Region. Because the instances run the most recent Amazon Linux release, they already support the EFS mount helper and NFSv4, so no file transfer between EC2 instances is needed — every instance reads and writes the same directories. EFS also scales throughput and storage automatically, which removes the availability problems caused by 25 GB files saturating a single EBS volume attached to one instance. This matches the two decisive constraints in the question: "available across many EC2 instances" and "across multiple Availability Zones". As xBUGx put it, "cross many EC2 instances and across multiple Availability Zones = EFS".
Why the Other Options Are Wrong
Option A (Amazon S3) is durable and Region-wide, but it is object storage reached over HTTP APIs; it is not a POSIX file system that an unmodified EC2 application can mount and use for 25 GB files with normal file semantics such as partial writes and locking. Option B is impossible as described: an EBS snapshot is a backup that must be restored into a new EBS volume before use, and an EBS volume attaches to a single instance, with multi-attach limited to io1/io2 volumes inside one Availability Zone — never across many instances in multiple AZs. Option D replaces durable storage with instance store volumes, which are ephemeral, physically attached to one host, and cannot be shared across instances or AZs; an AMI only captures the boot image, not shared data.
Community Comment Notes
Consensus on this item was unanimous, and the reasoning was consistently structural rather than memorized: mk168898 wrote that "files must be available across many EC2 instances" means you need "some sort of shared system" and immediately looked for EFS, while muhammadahmer36 repeated the same cross-instance, cross-AZ logic. One learner, freedafeng, raised the most useful counter-question — "why not A?" — which is exactly the S3-versus-EFS distinction this question is designed to test: S3 is shared and Multi-AZ, but it is not a mounted file system for existing EC2 workloads handling 25 GB files.
Official Reference
- https://docs.aws.amazon.com/efs/latest/ug/whatisefs.html
- https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-volumes-multi.html
These links open the official vendor documentation in a new tab.
Exam Strategy
When a scenario says files must be shared across many EC2 instances or across multiple Availability Zones with no copying between instances, EFS is almost always the intended answer for Linux workloads. Reserve S3 for object access patterns and static content, and remember that EBS volumes (and their snapshots) are single-instance, single-AZ resources.
Frequently Asked Questions
Why is Amazon S3 (option A) wrong if it is also shared and Multi-AZ?
Can an EBS snapshot or a Multi-Attach EBS volume serve multiple EC2 instances across AZs?
Community Votes
100% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 3 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 3
-
xBUGx 👍 6 Answered Ccross many EC2 instances and across multiple Availability Zones = EFS
-
freedafeng 👍 5my question is, why not A? I am fine with C
-
mk168898 👍 3 Answered C"files must be available across many EC2 instances" means need some sort of shared system immediately i look for EFS
Reader comments & corrections
No reader corrections yet — spotted an error or have a note? Share it below.
Related Analysis
Practice All SAA-C03 Questions
Access 120 questions with complete answers and detailed explanations.
View Full SAA-C03 Practice Test →