Answer: Amazon S3

## Explanation **Amazon S3 is the most cost-effective solution for this scenario because:** 1. **Massive Scale (900 TB)**: Amazon S3 is designed for exabyte-scale storage and can easily handle 900 TB of text documents without any scaling limitations. 2. **Cost-Effectiveness**: - **Amazon EBS**: Would require provisioning large volumes (900 TB) which would be extremely expensive and require complex management across multiple instances. - **Amazon EFS**: While scalable, EFS is more expensive than S3 for large storage volumes and is better suited for shared file systems. - **Amazon OpenSearch Service**: This is a search and analytics service, not a primary storage solution for 900 TB of documents. - **Amazon S3**: Offers the lowest cost per GB for large storage volumes with pay-as-you-go pricing and no minimum commitments. 3. **Scalability**: S3 automatically scales to handle any amount of data and any level of request traffic without provisioning. 4. **High Availability**: S3 provides 99.999999999% (11 9's) durability and 99.99% availability across multiple Availability Zones. 5. **Integration**: EC2 instances can access S3 through the AWS SDK, AWS CLI, or mount via S3 File Gateway if file system semantics are needed. 6. **Performance**: For periods of high demand, S3 can handle thousands of requests per second and supports parallel access from multiple EC2 instances. **Alternative considerations**: - If the application requires file system semantics, Amazon EFS could be considered but would be more expensive. - If low-latency block storage is absolutely required, EBS might be needed but would be cost-prohibitive at 900 TB scale. - OpenSearch is inappropriate as it's a search engine, not a primary storage solution. **Best Practice**: For large-scale, cost-effective object storage with unpredictable demand patterns, Amazon S3 is the optimal choice.

Author: LeetQuiz Editorial Team