The correct answer is Amazon Elastic File System (Amazon EFS).

Amazon EFS is a fully managed, scalable file storage service designed to be shared across multiple Amazon EC2 instances. It supports standard file system semantics, offers built-in redundancy across Availability Zones, and automatically grows as files are added. It is ideal for workloads that require shared access to file-based data and consistent low-latency performance across instances.

Amazon Elastic Block Store (Amazon EBS) provides block storage for a single EC2 instance (or a set of instances using special configurations like multi-attach for io1/io2 volumes), but it is not designed for concurrent access by multiple EC2 instances in the same way as a shared file system. EBS is ideal for single-instance use cases like boot volumes or application data disks, not for shared multi-server access.

Amazon S3 Glacier Deep Archive is a low-cost archival storage class optimized for infrequent access and long-term data retention. It is not suitable for active workloads or applications that require low-latency, file-level access across multiple servers.

AWS Backup is a data protection service, not a primary storage solution. Its useful for backing up existing storage resources like EFS, EBS, and RDS, but it does not provide direct access or redundancy for active file storage.

Why this question matters: It evaluates your ability to choose an appropriate storage service based on access patterns, durability, and scalability needs. Understanding the differences between block, file, and archival storage is critical for designing high-performing AWS workloads.

Tip: When you see requirements involving shared access from multiple EC2 instances and scalability over time, Amazon EFS is usually the correct choice, especially if file-level access is needed.

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