SAA-C03 Design Secure Architectures Practice Question
Several EC2 instances in different Availability Zones need to read and write the same shared file system. The file storage should stay available if one AZ has a problem. Which service should the team choose?
⚠ Common exam trap
Test-takers frequently confuse EBS Multi-Attach (which only supports a limited number of instances in the same AZ and requires a cluster-aware file system) with the true multi-AZ shared file system capability of EFS.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Amazon EFS
Amazon EFS provides a fully managed, scalable, and elastic NFS file system that can be mounted concurrently by multiple EC2 instances across different Availability Zones. It is designed for high availability and durability by storing data redundantly across multiple AZs within a region, ensuring continued access even if one AZ fails.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Amazon EBS
Why it's wrong here
EBS volumes are block storage that attach to a single EC2 instance in one Availability Zone; while multi-attach EBS exists, it is limited to a few instances in the same AZ and does not function as a general-purpose, POSIX-compliant shared file system. Because the scenario requires multiple instances across different AZs to access the same files concurrently, EBS cannot provide the necessary shared, multi-AZ access.
When this WOULD be correct
A single EC2 instance needs a durable, block-level storage volume with consistent low latency, and the workload does not require multi-instance access or cross-AZ resilience. For example, a database server's data volume.
- ✓
Amazon EFS
Why this is correct
Amazon EFS is a managed shared file system that can be mounted by multiple EC2 instances across multiple Availability Zones. It is a strong fit when applications need the same files at the same time and must remain available even if one AZ experiences issues. The service is highly available by design and reduces operational work compared with self-managed file servers.
- ✗
Amazon S3 only
Why it's wrong here
Amazon S3 is object storage accessed via a REST API, not a mountable POSIX file system; while it can hold shared data, it does not support file locks, arbitrary byte-range edits, or the low-latency file semantics expected by applications. To mount S3 on EC2, you need additional software such as S3FS or a storage gateway, which introduces overhead and still does not provide the same multi-AZ shared file system behavior as EFS.
When this WOULD be correct
When the requirement is to store and retrieve large amounts of unstructured data (e.g., images, videos, backups) from multiple EC2 instances, and the application uses S3 SDK or REST API rather than a mounted file system. Also correct for static website hosting or data lake scenarios.
- ✗
Instance store
Why it's wrong here
Instance store volumes are ephemeral block storage physically attached to the host server, providing high I/O but with no durability — data is lost when the instance is stopped, terminated, or the underlying hardware fails. Since the volumes are local to a single instance, they cannot be mounted by other instances, making them useless for shared storage across Availability Zones.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Amazon EFSCorrect answer▾
Why this is correct
Amazon EFS is a managed shared file system that can be mounted by multiple EC2 instances across multiple Availability Zones. It is a strong fit when applications need the same files at the same time and must remain available even if one AZ experiences issues. The service is highly available by design and reduces operational work compared with self-managed file servers.
✗Amazon EBSWrong answer — click to see why▾
Why this is wrong here
Amazon EBS volumes are tied to a single Availability Zone and cannot be shared across multiple EC2 instances in different AZs, so they cannot provide the required shared file system with cross-AZ availability.
★ When this WOULD be the correct answer
A single EC2 instance needs a durable, block-level storage volume with consistent low latency, and the workload does not require multi-instance access or cross-AZ resilience. For example, a database server's data volume.
Why candidates choose this
Candidates may confuse EBS with a shared file system because EBS volumes can be attached to one instance at a time, but they overlook the multi-AZ and multi-instance sharing requirements.
✗Amazon S3 onlyWrong answer — click to see why▾
Why this is wrong here
Amazon S3 is object storage, not a shared file system; EC2 instances cannot mount S3 as a POSIX-compliant file system for concurrent read/write access. It also does not provide file locking or low-latency file operations needed for shared file systems.
★ When this WOULD be the correct answer
When the requirement is to store and retrieve large amounts of unstructured data (e.g., images, videos, backups) from multiple EC2 instances, and the application uses S3 SDK or REST API rather than a mounted file system. Also correct for static website hosting or data lake scenarios.
Why candidates choose this
Candidates may think S3 is highly available and durable, and assume it can serve as a shared file system because it is accessible from any instance, overlooking the lack of file system semantics like locking and POSIX compliance.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
About these practice questions
This SAA-C03 question is part of Courseiva's 935-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.