What is the primary storage service for AWS's block storage?

Amazon EBS (Elastic Block Store) is the primary storage service for block storage in AWS. It is designed to provide highly durable, high-performance block-level storage volumes that can be attached to EC2 instances. EBS volumes are particularly well-suited for applications that require low-latency access to data, such as databases, file systems, and applications that demand highly consistent and predictable performance.

One of the key features of EBS is its ability to support snapshots, which allow users to create backups of their volumes that can be stored in Amazon S3 for durability. This means that EBS helps improve data resilience, enabling recovery from failures and facilitating data backup strategies.

In contrast, Amazon S3 is an object storage service ideal for storing and retrieving large amounts of unstructured data, but it does not support block-level access. Amazon Glacier is intended for long-term data archiving and retrieval, optimized for infrequent access, and is not a block storage solution. Amazon FSx provides fully managed file systems, which cater to shared file storage use cases but do not deliver block-level storage like EBS. Thus, given the context of block storage, Amazon EBS is definitively the correct answer.