A web application runs on Amazon EC2 instances in multiple Availability Zones and provides access to a repository of text documents totaling about 900 TB. The application will experience periods of high demand. A solutions architect must choose a storage solution that scales to meet demand and is cost-effective. Which storage option meets these requirements MOST cost-effectively?

Amazon S3 is the most cost-effective solution because it offers highly scalable, durable, and available object storage that can easily handle 900 TB of data and scale to meet fluctuating demand without requiring upfront provisioning. Its pay-as-you-go model and tiered storage classes (like S3 Standard-Infrequent Access or S3 Glacier) provide significant cost savings for large datasets. Amazon EBS is block storage, primarily for single EC2 instances, and would be extremely expensive and complex to manage at 900 TB across multiple instances. Amazon EFS is scalable file storage but is generally more expensive per GB than S3 for this scale of data. Amazon OpenSearch Service is a search and analytics engine, not primary storage for raw text documents.